Oil Watchman Power Tube Batteries

Here’s a little tip for anyone with an Oil Watchman tank gauge. If your batteries run out, you don’t need to spend £30 or so replacing it. You can open the tube and replace the four AAA cells that are inside, it’s a simple job – five minutes if you’re well organised, but allow half an hour if you prefer to take your time.

The power tube is the copper pipe sticking out of the unit that’s on your tank. It has a copper cap on the top, and the whole tube unscrews from the transmitter. You can replace the AAA cells inside simply by twisting off the cap, replacing the batteries, and then twisting the cap back on.

  1. Unscrew the power tube from your transmitter.
  2. Take a large pair of pliers that can grip snugly round the cap. Grip the cap with the pliers as near to the tip as possible (this prevents you from simply squeezing the cap tighter against the tube), and gently twist the cap off. A rubber-coated glove on your other hand might help you grip the tube.
  3. With the cap off, tap the open end of the tube gently on a hard surface and the batteries will come loose. They’re simply Duracell AAA cells, so you can replace them with shop bought batteries (the brand in mine were Duracell Procell, but this is just an industrial brand-name – battery chemistry is the same).
  4. Put the new batteries in, positive-end first. The negative end of the last battery will connect to the cap when you replace it.
  5. Twist the cap carefully back onto the tube, making sure it goes all the way on.

That’s all there is to it. You may want to put some grease on the the batteries as the Watchman manufacturer does; I didn’t bother, particularly since I have a bunded tank. If you want to be doubly sure of your work before screwing the power tube back on, use a multimeter to measure the voltage between the positive and negative contacts on the screw-on connector. You will see at least 6V if all is well, probably 6.5V.

Tips: I used penetrating fluid (WD-40 or similar) under the tube’s cap to help release it. If you still struggle, Brian Glanfield contacted me to suggest the clever idea of sliding a 15mm plumbing nut down the other end of the tube and then using a ring-spanner to hit the nut to knock the cap off. Since the tube is just 15mm copper pipe, it shouldn’t be too difficult to find a suitable nut (wide enough to slide down the tube, but not so wide it slides past the cap).

Someone has uploaded a video on YouTube (link) that shows the dismantled tube and discusses the details of removal and re-assembly (thanks to Jenny Edmunds for the tip-off!).

Also, if you have trouble locating a copy of the original Watchman manual, I have a copy here https://www.susa.net/docs/Oil_Watchman.pdf

Note on Oil Watchman Wall Plug

Although my batteries were low, and were overdue replacement, that wasn’t the problem that was preventing me from getting a guage reading. It turned out to be my wall-plug receiver. It was repeatedly showing three horizontal bars followed by the serial number of the device (this is on a barcode-sticker on the underside of the wall-plug, and will match the corresponding number on your tank transmitter).

The device seemed to stop working after a power-cut, and the problem may have been due to a surge when power resumed. This may be a red-herring, but in any case, I will try to make sure I switch the new unit off next time the power goes off.

I was able to order a new Oil Watchman wall-plug from the manufacturer (Sensor Systems/Kingspan Environmental) for £43 all-in price, which I decided to do in spite of the fact that I could get a new Watchman Sonic for just £10 more. I chose to stick with my original Oil Watchman because it has a physical tube to measure fluid depth, and so is much more like a sight-guage, and also because the Sonic’s lithium battery is only expected to last a few years – my Watchman’s batteries were still going after 8 years.

For technically minded, having opened the faulty device, it runs on a PIC chip (PIC16CE624) at 5V, and drives an RF-Solutions AM receiver module. The voltage from the output of the regulator is 5V, and the PIC chip was running fine. My guess is that the receiver circuit failed – either the receiver itself, or the supporting components. The voltage measured across the receiver’s pins was 4.5V, but it wasn’t particularly stable. Just a guess though, I didn’t have the time to look any more thoroughly. It’s a lovely little circuit, however, and has a beautifully simple and efficient AC-DC conversion circuit, so I’ll doubtless tinker with it when I’m bored one evening – even broken stuff has some usefulness in my house!

152 Replies to “Oil Watchman Power Tube Batteries”

  1. I have bought a used Titan oil tank that has the Watchman Niveau transmitter fitted, unfortunatelly i do not have the matching receiver.
    Will any Watchman receiver work, or does the receiver have a serial number that must match the tanks transmitter ?
    Also a thought, if a receiver goes faulty, and the pic ic is ok, i wonder if the pic could be swapped to another receiver ?


    1. You definitely need to match the receiver to the transmitter on your tank. I replaced my receiver after a power-spike killed the previous one, and I had to provide the serial number to the manufacturer so they could flash the PIC.

      The PIC will hold the serial number in EEPROM, so while it might be tricky to move to another receiver, it could work to repair a faulty receiver. With a PIC programmer, it might be easier to just read the EEPROM from the broken unit and flash it onto a working one.

      1. I suspected that the serials had to match, even to stop a neighbours transmitters data being “used” on your own (as they use the same frequency) !
        I also suspect the manufacturer has set the fuse set in the pic program so only the checksum can be checked, so stopping the pic being copied.

        I also do not know if the existing cutout on the tank that fits the Niveau model will be the same for a newer model or different make transmitter/sensor ?


        1. I had thought the EEPROM might have been left readable by a PicKit or whatever, but a quick look at the datasheet suggests it’s only readable by code which I agree will likely be protected.

          I’m sure I’ve seen the RF signal from the Watchman transmitter while working on something else – periodic stream of around 300 pulses. I forget the figure, but whatever it was, it was consistent and unlikely to be noise. A bit of fun to be had there – the protocol is probably trivial to figure out.

          You’d be easier just replacing the whole thing though – a complete WatchmanSonic might cost about £60 or so if you go back to the manufacturer and explain the situation.

          1. Thanks for the reply.
            If i replaced the watchman transmitter for say the newer model with the lithium battery, is tank cutout the same for both ?
            I have not been able to determine this.


          2. Sorry, the product naming I’d been using was wrong – Niveau is the old style (which I also have) and Watchman Sonic is the new ultrasound one with the Li-ion battery. I edited my replies to avoid confusing anyone else.

            I don’t know what the cut-outs are for the Watchman Sonic. The installation manual is here (http://www.sensor-systems.com/help.aspx), so you could check against either a Niveau manual (or just phone their technical line and ask). A drop-in replacement would seem to make commercial sense.

            However my decision in a similar situation was to replace the receiver for the Niveau, because I prefer the design – it’s more like a sight-gauge and uses easily replaceable off-the-shelf batteries that last in excess of 5 years. I could have had a new Sonic for about £10 more, but I think I made the right decision, and would recommend anyone do similar. The serial number needed to order a replacement is on the transmitter antenna.

  2. Regarding the reference to the failure after a power fault. I suffered the exact same problem late last year when the power came back on. No problem about getting a replacement from Kingspan though the power company did not want to know even though it was their fault that the power went off, this they admitted to me.
    Seems that there is a problem with the receiving unit that is prone to power surge.

  3. Kevin,
    As i still have not fitted the titan oil tank yet, i bought myself a used niveau receiver to play with.
    Looks like each half of the receiver case is glued/bonded together, when you opened it did you hack saw it, or did you open it another way ?


    1. I think I used a hacksaw on a corner then prised it open. However, the half with the plug-pins on it has a lip, and the cap with the LCD display fits over it – if you can get something under the seal, you may be able to prise it without cutting. The two halves look to have been stuck together with a brittle adhesive.

  4. We have a watchman and the receiver is constantly flashing red with what looks like a ‘r’ on the display…. We have replaced the batteries in the tube as suggested above, but display remains the same….any suggestions? I don’t want to spend £30 odd on a new tube if this is still not going to change display status…. Any suggestions greatly received

    1. When I switch my display on, I get three horizontal bars, followed by 4 digits, then another 4 digits, then it shows ‘r’ with the LED flashing every second or so. It’s waiting for a signal from the transmitter (the tube), but it can take a while before this arrives.

      If it doesn’t change after half an hour, then the transmitter is probably either faulty or has no power. The first thing I’d check would be the battery contacts inside the tube, in case a battery leaked and corroded it. I forget how easy/difficult is is to dismantle the copper tube itself – you might have to resort to using a torch to see, and something abrasive on a stick to clean.

      Also, try plugging the display into a socket that’s as close as possible to the tank, just to eliminate any chance of the distance or interference preventing the radio signal from getting through.

        1. Did you ever get yours to work as I have replaced the batteries in mine but still only get an r on the readout and light flashing every 3 seconds.

  5. I would like to thank you for saving me a good deal of money with the helpful tip of replacing the internal AAA’s, mine to were the Duracell batteries and I did have a chuckle now knowing that for £30 you’re getting a copper tube with AAA’s hidden inside.

    Excellent advice. However I had to use a flat head screw drive and a tac hammer to gentley tease the cap off little by little. Spot of electrolyte paste and Roberts your mothers brother!

    1. Thanks for sharing your tip. Yep, £30 does sound quite steep, but I guess the cost of providing a custom weather/condensation resistant battery box would also have been quite high – I suppose nobody’s retiring to the Bahamas on that particular revenue stream.

  6. Just used the excellent instructions on here to remove the copper cap but the contents spilt all over the floor! Unfortunately when I put new batteries in they don’t come up to the top of the tube so the cap can’t complete the curcuit. Have I lost a component when the cap came off?

    1. I don’t recall anything other than batteries and a connector in the copper tube. Perhaps try using a spring to complete the circuit. Let us know how you get on.

      1. Success! Worked at the second attempt. The spring I found was a little flimsy and I suspect the first time either I hadn’t tamped down the batteries or the spring curled up within the inner (insulated) tube. It’s easy to drift the cap off after all that practice! Existing batteries had ‘best before’ date of 2009 so I suspect they’d been in since tank installation in 2003 for previous owner.

    2. Did you loose the spring from the cap? I had to clamp the tube and after 10 minutes of gentle tapping used the reverse face of an axe! I found both cap and spring but alas after 30 mins am getting the ‘C’ error code for ‘Connection fault’

  7. I recently changed the batteries in my Niveau Watchman power tube after watching a video on Youtube,on the second attempt after making sure the spring was the right way up & the cap was all the way back on, it worked! also after a power cut the display changed to three horizontal bars followed by the serial number,then an r with a red flashing light.I thought it had broken so I tried unscrewing the power tube & then screwed it back on again & this rebooted the system & now it’s working fine again.Hope this helps others users.

    1. Thanks for sharing. I think the sequence of bars, serial-number, and ‘r’ is normal, and should change as soon as a tank signal is received. I usually unplug my receiver as soon as we have a power cut. I’m sure it was a power surge that fried my original receiver.

      1. Thanks for the info. I had the r, 3 bars and various numbers along with the flashing light..
        Changed the batteries as per your instructions and all works fine.

        If it hadn’t worked I would have resorted to the old method of dipping to see what is left.

        Thanks very much

  8. Despite replacing batteries I could not keep units working for longer than a day. After several attempts with multimeter and TNC T piece adapter I just happened to have, I supply the following tips.
    The tube connector is known as a TNC plug. A standard plug requires the knurling filed off. It’s a friction fit to the tube, so it can be pushed out with a rod from the other end of the tube. The original fit plug has a potted metal ring or contact on its rear to mate with the + on the battery. But hidden between the pin of the plug and its rear contact is a 33 ohm 1/4 watt resistor for IS purposes. (Intrinsic safety). In my case there was no solder between the resistor and the pin – so built in obsolescence! I used a standard TNC plug, some 2 part adhesive a nylon insulated spacer to make the assembly. I needlessly Dremel-ed my tube to remove the plug so had to use a jubilee clip to squeeze the cut pipe to make the negative contact to the plug. You do require a soldering iron and something to make the rear contact. Transmitter draws 7 ma at 6 volt

  9. Have just done battery replacement as per helpful comments/video etc after receiver seemed to stick on figure 8 for longer than expected (suspected ‘flat’ batteries in transmitter). However, that hasn’t done the trick (receiver still reading 8) so I’m wondering what to do next. We have had a few power cuts over recent months so perhaps the receiver is knackered? Incidentally, on checking the old battery voltages they didn’t seem all that lower than the new ones.

  10. Try a power off/on at the receiver, but with the power tube unscrewed. Leave for half an hour and check that no reading has been received (display unchanged in this time). Then connect the power-tube and wait for a reading.

    If you got an ‘8’ with no power-tube, then the receiver would appear to be faulty. If you only get an ‘8’ with the power-tube connected, then the transmitter may be faulty.

    I’d look at the assembly that sinks into the tank – as I recall, there’s a tube with a sensor at the top. I’d assume there would have to be an air hole to prevent the oil being held in the tube by a vacuum, so perhaps check that nothing is preventing the oil in the tube from falling.

    Of course, this is assuming there is actually a fault – mine can stay on a high number all summer – readings fall more slowly at higher levels.

  11. Many thanks for the information about the battery replacement. After considerable effort I managed to get the top off of the battery compartment, replaced the batteries and it works perfectly. Really appreciated, as I was already on the trail of a £30 replacement tube! Best wishes, Robin.

  12. Thanks for all the tips, I managed to twist the end off the tube as suggested, it was a bit of a struggle after ten years in the elements. I replaced the four AAA’s with new alkalines and also replaced the end cap with an “off the shelf” 15mm brass compression stop end fitting and some PTFE sealant. All worked in the end but it took about an hour for everything to re-set and work. We live out in the sticks ( hence the oil boiler ) and suffer from between two and ten power cuts a month, over ten years that’s quite a lot, but the sender seems to have survived them all, fingers crossed !

    1. Thanks for the feedback and the tips Trevor. Note that it’s the plug-in receiver that we suspect is vulnerable to power spikes.

  13. Hi
    My watchman keeps flashing ‘C’. I’ve changed the batteries as discribed, I’ve checked the spring, I’ve done a system reboot and it still just flashes ‘C’. Can anyone offer any advice please?


    1. According to the manual, ‘C’ means a connection fault at the transmitter. It does seem to be transmitting, so the batteries appear to be powering the transmitter. Check that the cables are all properly connected inside the tank, and that none of the connectors or cables have been damaged.

  14. hi all
    have simular problem with the 3 dash’s and s/n flashing. fault occured with a power cut.
    changed battery’s meter reading 6.3 v, removed tube and recaliberated system, refitted tube assy as per fitting instruction’s,note tank is 3/4 full, all to no avail. look’s like i need a replacement assy. any further update’s.


    1. Probably just the plug-in receiver that’s faulty – it costs almost as much to replace as to buy a Sonic version new, but I preferred the technology of the older version, and the batteries are easier to change.

  15. Hi,
    My watchman monitor was reading r so i replaced the batteries as suggested and when i re connected the transmitter the monitor was reading the oil level at 2, i thouht i had fixed the problem. When i checked again today the monitor is now flashing C….do you have any sugestions?

    1. The ‘r’ means there’s been no signal received at the wall-plug monitor (maybe the batteries didn’t need changed after all). The manual says that ‘C’ relates to a hardware problem. You should check that any wiring in the tank is properly connected and that the connectors are clean (e.g. mine has a wire between the sensor tube and the transmitter, I believe that some have the sensor tube connected directly to the transmitter).

  16. I was wondering if you could help me. I have recently moved into a house and have an oil tank for the first time. The read out seemed to work perfectly but then after a number of powercuts the read out only showed a couple of lines and not a number. I guess the powercuts have finally done for my niveau watchman.

    I tried rebooting the system, by turning the plug off and removing the transmitter.

    The readout is now seemingly working again, but is only showing a 4, when I filled the tank up recently and should be reading at least an 8 or 9.

    The readout is now flashing low battery. Do you think this is an issue with the watchman, or do you think I have been stiffed by the oil company? I cannot work out how I can look in to check its level. It is covered by heavy undergrowth making it very difficult

    Any help would be much appreciated



    1. It’s unlikely that the oil company ripped you off – you should have received a sheet with the delivered volume and details of the truck’s last calibration. It’s not impossible they mixed up addresses, and have delivered the wrong quantity to you.

      If the transmitter is reporting low-battery, then it’s possible that the workings of the sensor are affected, giving inaccurate results. Change the battery and see.

      Note, when the receiver is powered up (e.g. after a power cut), then you see what looks like an ‘r’ displayed until a valid signal is received fro the tank. This is normal, and doesn’t suggest a fault.

      You can always verify readings manually with a cheap tape measure from B&Q to measure kerosene depth inside the tank, and then do a bit of basic maths, according to your tank dimensions.

  17. Hi all. This site is fab. Followed instructions exactly and my receiver is now getting a reading which is superb! Only prob is that it is showing a 9 when the tank is less than half full. Any of you guys come across this? Perhaps I have not reconnected in the right sequence? ?

    1. Assuming nothing but the batteries have changed (e.g. any wiring and connectors securely reattached), perhaps the batteries themselves are giving too much voltage – are they ordinary alkaline cells, or did you go for lithium? I have read that the no-load voltage of Energizer lithium cells is around 1.8V, which could potentially throw the readings. The transmitter will be close to no-load, since it’s designed as a very low power device.

    1. There’s no mention of the indicator ‘P’ in the manual, but a search of Google suggests a couple of people have seen this before, so perhaps it’s an undocumented fault code.

      Try unplugging the wall unit and disconnecting the tank’s power-tube for a couple of hours to see if it recovers – power up the wall unit first, if the error shows up regardless of the transmitter being off, then it could be a faulty wall unit. If the error shows up only after reconnecting the power tube, then it’s probably a faulty transmitter.

      Sometimes faults are temperature dependent, so keep an eye on it to see if it recovers during warm periods of the day. In any case, if it turns out to be faulty, call Kingspan, who will probably be able to tell you what’s up.

  18. For those who don’t have a plumbers nut of the right size to hand I had great success with a jubilee clip.

    Also the pro cell batteries are much cheaper than normal duracells.

  19. Can anyone help? my watchman was occasionally flashing ‘C’ but then would resume with the level. I blamed birds going in and out of hedge and maybe interrupting the signal but now has been flashing ‘C’ for some weeks. I have not noticed that the wire which was beneath the power tube (not sure if it is an ariel?) is missing anyone know the name of it so I can search online for a replacement?

    Any help much appreciated.

    1. I checked my tank’s sensor – I have a bunded tank and there are two wires coming from my transmitter. One is a black length of coax that connects to the depth-sensor, and the other is a white wire that connects to the bund-sensor (a spiky ball that I assume contains a switch that operates if there’s a leak into the bund).

      Status ‘C’ means connection fault. The bund sensor wires are joined using bullet connectors, so I suppose these could come loose. It not impossible that deposits could form on the connectors, causing a poor connection. If the bund-sensor wire is completely missing, then it may have fallen to the bottom of the tank. I can’t tell if it can be reattached.

      If the wire you’re referring to is the coax for the depth sensor, then it may be broken – it’s difficult to imagine how this connector could work itself off, since it’s much more substantial than the bund sensor wire.

      1. I can confirm that my system faulted to flashing “C” and it was the twin bullet connector from the lead down into the bund that had developed a poor connection. I connected/disconnected a few times to try to clean it up and then all was well.

  20. We have changed the batteries in the copper tube but we get a C on the receiver, we have looked inside the tank but there are no wires, just the long tube and the hole on the side is clear, is the sensor in the bottom of the copper tube where the batteries are or is it somewhere else can anyone help us to locate the sensor. It would be a great help.

    1. Working from top to bottom, there’s the copper tube, which screws into the sensor housing (dark green plastic cylinder) which is screwed onto the tank. Under the sensor housing is a hole in the tank, through which a black plastic tube goes down to near the bottom of the tank. That’s pretty much it. The sensor sends clicks down the black plastic tube, measures the time taken for echoes to return, and calculates the fluid depth.

      The version for a bunded tank is slightly different – it has the sensor mounted on the inner tank, and some coaxial cable connects to a transmitter (with similar housing, so it looks very much like the sensor) with the power-tube screwed on. This is really just to allow more flexibility on the transmitter placement.

  21. Many thanks for these instructions (and also to the gentleman who provided the YouTube video). When returning to the house after a power cut I found the receiver showing an r reading and when I removed the original batteries from the power bar I noticed the expiry date was 2010. In my case, after reassembly and reinstalation of the battery pack as per the instructions, the receiver stubbornly remained on a r reading whatever I did. Eventually sorted by disconnecting the battery pack, turning off the receiver and taking out of the socket, wiping the receiver’s plugs with a cloth, reseating the aerial and waiting for 2 mins, plugging that back in and waiting for it to show r, reconnecting the battery pack and leaving for a couple of hours the system started to work again. I don’t know if any of the above contributed or wether it was just a matter of being patient while the receiver acquired the first signal. Anyway £30 saved, thanks very much.

  22. I wonder if you can help. We have a bunded tank and a niveau plus watchman. We’ve changed the batteries and put thh tube back into place. On the second attempt there was a buzzing noise as my husband put the tube back on, and our display worked showing a 6. We thought we’d sorted it out but 24 hours later the display went back to C. We’ve re checked the batteries, spring, etc, and each time, it goes back to C.. Any suggestions?? We haven’t seen any cables that we’d need to check…

    1. The buzzing noise is normal – it’s the ultrasound sensor sending ‘clicks’ to read fluid depth. I’d be looking to clean connectors – with a Niveau Plus there will be a white (on mine at least) wire to a spikey plastic ball lying on the floor of the outer tank (which senses leaked fluid). There’s also a connector between the transmitter (where the battery tube is connected) and the depth sensor. If all this is wired up, and there’s no build-up of corrosion on any of the connectors, then I can’t think what the problem might be.

  23. Hi folks, I need some advice on the wall receiver for Watchman Niveau. The batteries needed replaced, so replaced the four AAS batteries with Durecell Procell in the transmitter tube. Receiver wall socket showed an “r” with red light flashing. Reconnected the transmitter tube and got the level to appear. Job done (or so I thought). 24 hours later, both the fluid level and red light started flashing on receiver wall socket. Tried resetting and level appeared again, it worked fine until 24 hours later. Can anyone please advise why the fluid level and red light are flashing on the wall socket receiver 24 hours after reset?

    Many Thanks,


    1. If the receiver fails to get a signal for a full 24 hours, it flashes to warn you. Check for a clean connection in the screw-on tube connector, make sure all your batteries were fresh (still got the old ones to measure, to make sure none got mixed up?) and that no other wiring came loose while you were working. Also, with some cheap batteries (or eBay rip-offs), the cells can drop voltage quickly in cold conditions.

  24. Thanks for this free information on how to change the batteries. Its kind and knowledgeable people like you that help people save money and prevent landfill.

  25. Excellent article and clever tip sliding a plumbing nut onto the tube to tap off the end cap. Got the whole task completed in about 10 minutes for the cost of 4 AAA Duracell batteries. Great saving on the £38 + vat and delivery that I was about to spend!

    Cheers guys, much appreciated.

  26. I acquired property in early Nov 2014. Watchman Niveau Plus Receiver was showing a steady reading. From early Dec, after some power cuts, the receiver flashes, alternating between a reading and c. however the reading does seem to be accurate and has changed over time, including when new oil was delivered. I changed the power tube batteries for the cost of the 4 batteries following the very useful advice from the site. Whilst I had the power tube unconnected the reading continued as before and also once I had refitted the tube.
    I do seem to be getting correct readings but how can I stop the flashing? Should I just try switching off the receiver and then starting it up again or will I need a new receiver?

    1. From memory, I think the manual says that a flashing C indicates a wiring connection problem. I would check that the bund-leak sensor connectors (bullet plugs) are firmly connected and free from corrosion. Since you are getting valid level readings, it would seem likely that other connections are fine.

  27. Just to say “thanks”for the instructions on changing the batteries. Very simple. It never occurred to me that the copper top would just be tapped on.

  28. How do I know if the batteries are running low as Yesterday my RX model was reading 9 on the plugin receiver and today a symbol resembling the letter [ r ] is showing , and I cant find my instruction manual to find out what it means.

    1. This shows when the receiver is waiting for a signal after being switched on. Try plugging it in somewhere closer to the transmitter. The manuals can usually be found with a bit of search engine trawling (tip – include ‘pdf’ in your search terms). I have PDFs somewhere if you draw a blank.

  29. Hi there – quick question, I hope someone can help! I have a lower-case flashing ‘c’, which intersperses with the number ‘7’, which I think is the level of the oil. The instructions say that a display specifically of a ‘capital C’ means connection error and this is definitely a lower case. Also, if there was no connection, presumably it wouldn’t also be showing me (what I assume is) the level.

    If anyone could help, that would be great.

    1. Connection in this case refers to the wiring of the transmitter assembly – the model of Watchman designed for a double-skin tank has connections for the leak-detector sensor and for the fluid-depth sensor. Since you seem to be receiving tank readings, I’d look at the bullet-plugs that connect the leak-detector. Maybe they’ve accumulated some corrosion or come loose.

  30. After much experience of Haynes manuals in my formative years, I am always a bit sceptical when something is referred to as an easy 5 minute job; but actually this was for me… Watchman unit was installed about 10 years ago and the power tube voltage was down to about 4.6V (4x individual Duracell Procell dated 2012), causing the indicator light to flash and showing intermittent readings. In case it helps anyone, an alternative way to remove the cap is to secure a 15mm ring spanner firmly in a bench vice, slide the power tube into it up to the cap and sharply pull the tube; comes off a treat! Take a little care to line up the cap when refitting, but it goes back on again easily enough with a gentle tap from a mallet. Only problem is what to do with the extra 6 batteries – I bought 10 (the minimum quantity) Industrial Duracell AAA batteries for the princely sum of £2.20.

    1. Thanks for pointing out my blasé use of language! True, it can be a 5 minute job, but more likely half an hour all in, assuming the tools and batteries are available.

  31. I have a Watchman Plus which is flashing the upper case ‘C’. Having read the instructions it says there is an internal fault and damage may have occured. Do you know how or if there is anything I can do? Also, I bought our house with this system and do not know where I can this sorted. Is this an oil heating engineer job? Thank you

    1. The ‘C’ denotes a connection fault, so the wiring may be faulty, or perhaps just dirty or corroded connectors. See the other comments for a little more detail.

      It’s a fairly simple system, so no need for an engineer unless you really can’t be bothered, in which case I’d start by asking your boiler service engineer. Now is not a bad time to get it serviced, if you’ve just moved in and don’t know the history of your boiler.

  32. I have an apollo ultrasonic receiver and need to replace the battery in the oil tank. All I need is a 3V-CR2430 battery to put in the transmitter, can you please tell me where I can obtain one as they don’t appear to be available in my local shops? Thanks in anticipation of your help.

    1. Just put the term CR2430 into your favourite search engine, and there are lots of online vendors selling them for around £2 including postage.

  33. I have a Niveau unit which has had new batteries a couple of times (btw, worth reminding people to lube them with Vaseline so they come out again) but the latest change has not got rid of the little “r” shape. It did briefly show a 0 despite tank having 800 litres in it; then it showed only the r and a flashing light. Receiver seems OK so am beginning to suspect the sender unit is faulty. Any tips before I order a new one?

    1. Check for build up of corrosion anywhere there’s a connection, and that the batteries are making good contact. The spring on the negative contact needs to be clean, as does the inside of the copper cap that it touches. The kitchen scourer should be good enough. Also, no harm checking that there’s not Vaseline on the battery terminals.

  34. Many thanks for this, just replaced the batteries in my powertube and all is working again..eventually.
    Basically After replacing the batteries (exp Mar 2009!) I had it working giving me a reading of 7, being curious I removed the whole unit to see if there was anything that may have caused a C error I get on a hot day, nothing obvious I replaced it and tightened the mounting screws.
    Upon switching on the receiver unit I get the r message (awaiting signal) replaced by the C error that took a lot of effort to resolve, I have the version for an UN bunded tank, so just the transmitter with the empty tube below, no other connections.
    If anyone else gets the C error after removing /refitting the transmitter from the tank, try loosening the mounting screws a fraction.
    This is what my issue was, it would also explain the C error I would get in hot weather as the plastic expanded squeezing the joint and inducing the C error, that would rectify itself upon cooling!
    I know this to be the answer as I took the receiver out to the tank on an extension lead whilst returning the C error and loosened the screws a 1/4 turn each, error gone, tighten a 1/4, error returns.
    All working now and still secure enough not to allow water ingress.
    Anyhow, thanks again and pass it on.

    1. Quite a curious problem & solution. I guess that either the tube squeezing on the ultrasound transducer might add stress to the circuit board or solder joints inside. As far as I can tell, the transmitter case is filled with epoxy, so perhaps stress to the casing is causing stress to the electronics. In any case, interesting information, thanks for sharing.

    1. Thanks for the link. I’m not particularly tempted by the Watchman Sonic from a user perspective – no added benefits, though I’d probably enjoy decoding the signal.

  35. Have only just found this very informative site. Wondered if anyone has had the same problem as me. My watchman is constantly flashing and registers an upsidedown L all the time. I will be asking my service engineer to fit new battery when he visits soon, the last one only lasted 2years so think I may need to re-place, but as I did not receive a manual when my new tank was delivered complete with watchman in 2007 , I have no way of knowing what this upsidedown L means. Would be grateful if anyone can advise me.

    1. You’re probably seeing what’s meant to be an ‘r’ – this means no signal has been received from the transmitter since switching on the wall-plug display. For testing, I’d temporarily plug it in as close to the tank as possible (maybe even use an extension lead if needed). The tank unit should send a signal within an hour.

      I’ve put a copy of the PDF manual here http://www.susa.net/docs/Oil_Watchman.pdf – it lists the error codes and meanings.

  36. I never have a problem with power surges messing up my Watchman plug-in reader – I don’t leave it plugged in! if my tank is filled in say July, I might plug it in sometime in November to check levels – I get the ‘r’ which I interpret as ‘reading’ the level, and once I know I’m OK for a while longer, I unplug it and it goes back in the drawer. We use a socket in the kitchen (nearest the tank) but with a lack of sockets in that area, not leaving it plugged in frees up a socket – and all the while the sender is not talking to the plug I suspect the batteries are dormant also. Naturally I know roughly when to check levels with it being a house we have had for 8 years – early stages I checked more often.

  37. Thanks Kevin for an informative article
    I have a bunded tank and have just replaced the batteries and all is back to how it was before
    However previously I had the flashing “c” with the number and didn’t realise what to do. I have now checked the bullet connections but the “c” is still flashing with the number.
    Do you know if the bund sensor is normally open or closed.
    If closed could I short it out at the bullets

    I shorted it out but there is no change
    I suspect that the transmitter is faulty or there is a break between the transmitter and the bullets

    1. My own watchman is also giving me some intermittent problems. It sometimes fails to transmit for more than 24 hours and also gives me a leak-error indicator. It goes back to normal after a few days.

      I haven’t figured out if it’s cabling, or something inside the unit, that’s at fault – the epoxy filling makes it tricky to diagnose, but I’ll report back when the milder weather returns and I get a chance to have another look.

      I’m not sure about the bund sensor – it may even be an analogue input (resistive?) rather than digital open/closed. I haven’t checked, but if there’s a constant 0V or 5V across the pins, then it’s probably digital. If a periodic voltage is seen on the pins, then it’s analogue (in which case, it may look for specific resistances for all-good, leak-detected, and error values).

  38. I have just checked with a multimeter and I don’t have any voltage across the pins from the transmitter, it’s a steady “0” DC voltage

  39. Recently bought this property with the monitor already fitted. When plugged in, it was showing the flashing red light and the ‘r’. I purchased a new power tube and successfully fitted it. The receiver then picked up a signal of ‘4’. All seemed ok. However, visited the property a few days ago and I now have 3 horizontal lines on the monitor. Can anyone explain what this means and what can I do to solve it? Thank you.

    1. I seem to recall (though I may be wrong) that this was the symbol that showed when my wall plug failed. I never got to the bottom of exactly what the problem was, but I just bought a new wall plug from Kingspan. Really, the only course of action is to unplug the wall plug & disconnect the powertube and then power it all back up. If that fails, then my guess is that replacement is the only other option. The replacement must match the serial number of the transmitter, so you have to get it through Kingspan. They will probably recommend you buy a Sonic instead, they may be kind enough to credit you for the new powertube if you choose this option.

      On a technical note for anyone interested, the PIC chip seemed fine, and I used the RF receiver module in another circuit without problem, so that didn’t seem to be the problem either. There’s little else in the circuit. One possibility is a voltage spike erasing part the EEPROM memory on the PIC chip, or perhaps blowing one of the input pins. The serial number was still showing when the unit was switched on, so at least that part of the EEPROM was still intact.

  40. I contacted Kingspan Customer Services before finding this site
    This was there reply

    Good afternoon Mr Wiseman

    Thank you for your email.
    We no longer manufacture your unit. It has been replaced with the Watchman Sonic, a direct replacement for the plus and will fit into the same mounting. This can be purchased locally or from ourselves for £73.00 including vat & p&p

    Kind Regards


    I replied saying I wasn’t happy with there response
    There reply was

    Good morning Mr Wiseman

    I am extremely sorry you feel like this

    Kind Regards

    I don’t think you will get any support from them

    1. To be fair, they have simply revised their product line and are now making the older products obsolete. It may be that they simply don’t have any saleable parts left for their old products, other than the powertubes that they doubtless feel obliged to continue to produce – I expect there’s still profit to be made on these, but low volume runs to stock up on spare transmitters and wall plugs would be expensive.

  41. Hi all,

    I have a watchman plus which is currently showing a flashing C.

    The connection between the coaxial cable and the transmitter is broken; for some reason the compression fitting doesn’t unscrew and so I will need a new one and then i will prep the coax. appropriately so as to make a new connection.

    Does anyone know the spec of the coax cable and the compression fitting?

    I could buy a new watchman sonic but I don’t see the point in throwing it all away if it is just the connection.

    Also, the coax cable is tiny so would it be wise to up the spec of the coax section of the system?


    1. For the cable, any 50ohm coax should do (I’d even guess that 75 or 100 ohm cable would work at such a short distance).

      I don’t have a part number for the coax connector. However, on a (non plus) transmitter I have, the connector has an external diameter of 9.6mm (11mm including the thread), and 8.5mm or thereabouts internal diameter. I would check Farnell or RS to identify something that looks similar and check the datasheet’s measurement diagram. I’m sure they’re pretty standard parts.

      Take care when removing the old cable if the connector is seized on. As I recall, all electronics are embedded in epoxy – if you damage the connector on the unit, then I think it might be difficult to replace.

  42. Since posting the above message, I have done some research on coaxials. I would like to correct my post by saying the connection between the f connection fitting and coaxial is broken. The reason it twists as I suggest is that it is a twist-on variety of f connector – I hadn’t understood this – oops!!

    I need to strip the coaxial and prep it to re-establish the connection so I hope this will do the trick! I will give an update in due course…

    If anyone knows the spec of the coaxial I would still be interested to know!

  43. Display readout is constantly changing.
    I’ve removed the battery pack, replaced the batteries and checked the voltage is OK with the new batteries – but have not yet connected it.
    Switched off the receiver and then switched on again.
    Every 2 secs I get a flash of the red light, for 4 repeats during which time it displays various digits.
    Every 5th repeat the red flash is brighter and longer and is followed by three horizontal bars.
    Then repeats the process again, and again….
    Have connected the new battery pack but nothing changes.
    Assume it’s the transmitter or receiver not working. Any way to check?

    1. I believe something has failed in the receiver. The digits shown in the sequence should correspond to the serial number of your Watchman. You used to be able to get a replacement receiver that is programmed with this serial number, but the price is similar to a new Sonic version, if even available these days.

      This happened to me some years back. Technically, the PIC chip that controls everything seems OK, since it is driving the display which is working correctly. The RF receiver module was also tested and worked fine. The DC power supply was seemingly OK too. There’s little else significant on the board. My guess would be that one of the passive components (crystal for the oscillator, a capacitor, etc.) had failed.

      Regardless, without a bit of tinkering knowledge and soldering skills, there’s nothing that can be done to fix it.

  44. Watchman

    Firstly thank you for posting this very useful and money saving info. I have a strange problem and thus a couple of questions. I have a watchman Plus on a bunded tank – both new in 2004. From day one, the receiver has flashed a small ‘c’ and the tank reading. I contacted the supplier and they send out a replacement transmitter and receiver – a watchman rather than a watchman plus. Anyway as I was getting correct tank reading in between the flashing c I decided I couldn’t be bothered to mess about in the tank so have just lived with it. A couple of weeks ago we had a power cut – this managed to upset one of the heating system’s programmers and I have a boiler man coming to install the replacement on Thursday. Then we had another power cut a couple of days ago! This seems to have fixed the programmer and affected the Watchman receiver. Like a previous correspondent we frequently have power cuts and the Watchman has never been affected before. Basically it has stopped flashing ‘c’ and is just showing me a steady 5 which is probably about right. If I unplug it, it initialises, flashes red lights and after a while goes to 5 and stays there. So my first question is is this how it should work normally? It never flashes the red light now which makes me think it’s not attempting to find the latest reading – should it? All I can do at the moment is keep an eye on it and see if it drops to 4 which given the temperature just now shouldn’t take more than a couple of days.

    Given that it seems to working now should I change the batteries? If it ain’t broke …. but on the other hand these batteries are at least 12 years old now. Can’t believe they’ve lasted this long.

    Or should I use the ‘replacement’ watchman they sent me in 2005 after changing the batteries in that one?
    And can I replace a watchman plus with a watchman?

    Any advice gratefully accepted
    Thank you

    1. Sounds like a cartoonish sequence of events! It does seem to be working as would be expected – it has received a signal and is displaying the level. The ‘c’ is, I think, a connection problem being reported by the bund-leak detector. Can’t imagine why it would incorrectly show an error until after a power cut, perhaps whoever came out to see the programmer checked the wiring, and the second power cut cleared the old error?

      The Watchman would be difficult to fit on the tank directly, since the antenna (powertube) doesn’t fit within the outer skin of the tank. Maybe the existing coax cable could be used as an ‘extender’ to bring the powertube/antenna to a suitable place? I forget the connector types on each part of the transmitter – you’d have to have a look.

      Still, if you’re confident your readings are valid for your tank, I’d be tempted to just leave exactly as is. If you have a spare Watchman, you can use the spare powertube when the current one finally runs out, giving you plenty of time to replace the batteries in the old tube.

  45. I have a Watchman Plus (Tank Contents Level and Bund Monitoring) fitted to my Titan ES1225B tank – all fitted new in Dec 2006. A few weeks ago the receiver started flashing C, together with a constantly flashing red light. I hoped this was a temporary blip so ignored it (!) – but several weeks on, and despite numerous unplug/replug attempts (in sockets of varying distance from the tank), I still can’t get a reading. This is problematic as the tank has no other means of checking oil level (e.g. an external gauge) so I’m entirely reliant on the Watchman telling me how much oil I have.

    In this thread a lot of comments relate to changing the batteries in the copper tube ‘antenna’ – but my Watchman system doesn’t seem to have one. The system is fitted to the inner tank, under the access hatch on the outer tank so I don’t see how an antenna could ever have been fitted as it would clash with the hatch lid. All I can see inside the access hatch is what I think is the top of the transmitter fitted into the inner tank – attached to which is a black cable that runs down into the space between the inner and outer tanks. I think this might be the bund monitor? I took some pictures in the hope that someone could perhaps tell me what’s what – but I can’t see any means of posting pictures here.

    So – I don’t know if the reason for the system not showing me how much oil I have is that the batteries need replacing (if so – where are they if I don’t have a copper tube?) or that I SHOULD have a copper tube but it’s fallen off/ been removed during a delivery and lost, or that the system is just broken and I need to replace the whole thing?

    Any advice or suggestions would be enormously welcome. Please assume (correctly!) that I have zero DIY knowledge/skills. If any work needs doing beyond simply changing batteries I’ll need to call in a pro to avoid the risk of me blowing me and my neighbours to kingdom come!

    1. The Plus model has two parts that are similar in shape. One is mounted on the inner tank, and has the black cable you mentioned connected to the second part that is the transmitter with the powertube (batteries and antenna combined) screwed into it. Sounds like your transmitter is dangling down the side of the inner tank. Pull this up (carefully, in case it snags on something) and mount it properly.

      If the cable comes up empty, then maybe the transmitter is on the floor of the outer tank. A torch and a litter picker might be needed! You can also use a torch to look into your tank to get a rough idea of how empty it is.

      Incidentally, Kerosene doesn’t burn anywhere near as easily as, for example, petrol that quickly evaporates explosive fumes and burns vigorously with a mere spark. I’ve read that a lit match falling into a bucket of kerosene would simply go out. Obviously take care because it’s a messy and toxic fuel that would be flammable if soaked into fabric, but don’t worry too much about tank explosions and such.

  46. Thank you SO much for replying so quickly and for taking the time to give me your advice.

    I’ve investigated further (ladders and head torches were involved!) and can now just see the transmitter (brass tube type thing) on the inside of the outer tank. Unfortunately, the transmitter is secured to the tank skin on a bracket so I can’t just pull it up to try to replace the batteries and I can’t get at it to work on it in its current position :-(. Even if I could get the transmitter OFF the bracket, I’d have no way of putting it back ON the bracket after I’d (hopefully) fixed it and wouldn’t want to leave it dangling…

    It looks like the monitor was fitted before the ‘lid’ of the outer tank was positioned and secured so I suspect this lid needs to be removed before anything can be done about the monitor. That’s too big a job for me (one side of the tank is relatively close to a wall that precludes ladder access and I’m not confident enough to climb onto the tank to release/replace the fittings from above!) so I’m going to have to call in someone to help.

    Thank you again for your advice. Although I haven’t fixed the problem at least I now know where everything is on the tank and what I need someone to help me with. I also peeked inside the tank to check the level and have ordered more oil! I really appreciate your help – the internet is a wonderful place sometimes 🙂

    1. If you can reach the bracket with something to prise it off, it’s actually quite weakly secured with soft plastic plugs (and plastic screws as I recall). It doesn’t have to be remounted in the same place.

      However, I’d be tempted to simply fit a new monitor to the tank rather than get someone to fix the old one. The monitors themselves are cheaper than labour costs required to get access to the old monitor (unless you’re getting a friend to help, of course).

      1. The oil engineer is coming out to service the boiler next week and is going to ‘have a look’ at the monitor situation for me.

        I agree with you – if it’s going to take hours of faffing about to get the old monitor out to replace the batteries and/or fix it (that is, of course, assuming it’s fixable) I’ll just buy a new one, which will hopefully last me 10 years like this one did!

        Thanks again and Happy New Year!

  47. I replaced the batteries in my power tube with standard Duracell batteries but they only lasted about 6 months whereas the originals last 10 year from the time the tank was installed. Is there a better type/brand of battery that should give me longer life please ?

    1. I once read that the industrial Duracell batteries are identical to those that are retailed, and that the colouring is different only to avoid bulk-priced packs being re-sold at retail pricing. That seems plausible to me, since the chemistry is well understood, so I’d guess that fresh Duracells are about as good as you’d get.

      I’d check for one bad battery (rare with Duracell, in my experience, but it does happen). I’d also consider whether they came from a reputable source (e.g. not counterfeit), and check their expiry date if possible.

      After this, I’d clean the battery terminal connectors and screw threads (spray WD-40 and scrape with an old toothbrush and/or flat screwdriver). Dirt and corrosion can increase resistance, which could show as a lower voltage from the batteries.

      Of course, it could also be that the Watchman is faulty and is now simply drawing more current that it should be.

  48. First thank you Kevin for all your help and advice.
    I have just replaced the batteries in my power tube, success at the third attempt. I had to use a blunt chisel to get off the cap and found the batteries were a loose fit. On refitting the tube the r signal returned. I searched around on the floor and found the missing cap Spring needed to make the contact. When fitting it it seemed unstable with the point towards the batteries but stable when reversed so I refitted it in the stable position. Again the r signal. Finally I fitted the cap spring with the point towards the batteries. Success is heartwarming. Many thanks.

  49. Hi, Just moved to a house with oil and so its new to me. There is a transmitter on the tank but no receiver. The oil engineer gave me an old unit to try. It seems to flick through some numbers and then stay on’L’. Do I need a new one? thanks

    1. You’ll probably need a completely new sensor. The transmitters and receivers are paired so that the receiver only displays readings from its corresponding transmitter. It used to be possible to buy replacements from Kingspan, where you quote existing the serial number and they send you a suitably configured wall-plug, but I don’t think they do this any more.

      It’s quicker and cheaper to just buy a replacement Watchman or Apollo.

      If you’re technically minded, and familiar with PIC chips, then there’s some fun to be had attempting to re-program the EEPROM on the unit you were given. However, it’s a bit of a long shot.

  50. Hi. I have the same system. It constantly shows full when it isn’t. Inherited the system when I bought the house. Changed the batteries as suggested (brilliant info thanks). Any ideas. I have. Checked and tubes etc all seem clear and all plugs are working because if you disconnect it shows fault.

    1. Check there’s nothing blocking the ultrasound transducer, which is where the tube joins the transmitter. I suppose that corrosion on the metal disk of the transducer would prevent it from flexing properly, so a torch should help show a nice shiny surface (or not, as the case may be).

  51. Replacing AAA batteries not as easy as it sounds. I’ve tried it twice – once without Vaseline and once with – although I did get it to work once for about three months. No luck at all now

  52. Hi ,can I just say what a helpful site!Kevin I have removed the cap from the powertube and replaced the batties.
    The sensor is showing three horizontal dashes.I noted the ariel at the top seems loose and twists round easily without tightening.Is this normal.Also is there supposed to be a spring inside the cap of the copper tube?

  53. Hi, after successfully replacing the bateries and checking I had 6+ volts to the sender unit, the reiver continues to flash and the bat low message is still lit.
    Can you help?

    1. Since the sender is filled with epoxy, so far as I can tell, there’s not much that can be done practically on the electronics to troubleshoot. Other than dirt/corrosion on the metal of the contacts, it might be that the problem is with the circuit that measures battery voltage (e.g. perhaps the unit is incorrectly reporting low battery).

  54. Ouch! I’ve dropped my battery power tube inside the outer casing! I can’t even see it. Does anyone know a way of retrieving it please (they are copper so a magnet will not work)

    1. I’d start with a torch that has a reasonably directed beam (e.g. most LED torches), and one of those flexible drain cleaners (springy steel band you uncoil to use) that can be had from most pound shops. Poke around until you can at least see the tube. Then, a kids fishing net might get it out with a bit of persistence. Or perhaps a litter-picker, modified with two halves of an old kitchen sponge stuck to the inside of each pincer (i.e. to give a wider grip surface). Or some combination of the two – you’ll need to get creative!

  55. This is such a useful and comprehensive site. Our tube needed new batteries, which we have managed to do with the aid of a kind neighbour, but I can’t make them reach the top of the cap even when using a mallet to push it down. I think I must have thrown away a spring, stupidly. What could I use to replace, have you any ideas please?

  56. Can anyone assist, I have a watchman and the “plug in “ receiver reading in the house is `r` followed by a red flash every 5 seconds!
    I have changed the batteries, used a different plug socket in the house but nothing changes! Very frustrating as it is difficult to “guess“` as to the oil content in the tank without resorting to the old “dipstick“method.

    1. The docs might help. I have a copy here if they’re now hard to find on the official site – https://www.susa.net/docs/Oil_Watchman.pdf The ‘r’ means the receiver is waiting for a signal from the transmitter. Try plugging it in as close to the tank as possible, line of sight would be good too, if at all possible. If you can check the voltage coming from the power tube, then that would at least confirm the transmitter is getting power.

  57. I know this is an old post but hey I’m a newbie and need some advice on an old problem.
    During the recent hot weather my oil watchman started flashing the red light and displaying the dreaded ” C “, but after turning off and on again 5 mins later it went back to normal. However now it just flashes red and C is permanently displayed. I’ve changed the batteries but to no avail. What could have happened in the sunshine to have k n ackered it. It’s the older style with dip tube and wire connecting dip tube to sender unit. I’ve also got a spiky ball between the walls of the double skinned/bunded tank which I guess is leak detector/alarm.
    Can anybody shed some light on whats happened ?

  58. Kevin, this has been very helpful, thank you. Error C on Watchman Plus, cleaned connections to bund “sensor” and that fixed it. My battery tube is at least 12 years old and still functioning!


  59. Hi,

    I have inheritied a Watchman Plus system for the oil tank when we bought out house. (Never had an oil tank before). All was working well until recently (4 weeks ago) when I get a rapid flashing red light and a capital C on the display. I changed the batteries in the power tube. Still have the C. Can anyone please help. I have tried to contact supplier Sensor Systems in Lurgan Northern Ireland however they appear to have ceased trading. Also does anyone know if there is a company out there who will fix such a syatem as I am completely lost here. I live in South Norfolk.
    All replies appreciated.

      1. Is my transmitter broken? Is there anything I can do apart from buying a new one?
        I have a Niveau Watchman, with a flashing uppercase ‘C’. I have replaced the batteries using the excellent info on this site. If I disconnect the battery tube from the transmitter and then turn on the plug it boots to a flashing ‘r’, (waiting for a signal from the transmitter). When I connect the battery tube to the transmitter I very quickly get the flashing ‘C’ . So I believe the transmitter is transmitting (because getting the ‘C’ coincides with connecting the battery) but seems to be faulty. I tried loosening the screws on either side of the transmitter as mentioned in one of the posts above but this made no difference. What is the springy wire on the transmitter, I assumed this was an aerial but others have mentioned that the tube is?

        1. A flashing ‘C’ indicates a connection problem. There are only a few different connections on these units, so it might help to disconnect what you can, clean the connections and reconnect. The springy wires on the transmitter are the ground plane for the antenna, which is indeed the power-tube itself.

  60. I am getting the usual sequence of messages on the wall unit, but then it defaults to a P with an upside down P beneath it. No help to be found in Watchman instructions. I have renewed the batteries in the tube. I have had the unit at least 12 years, so it’s not a surprise it needed batteries! Have I missed an explanation of this in the earlier (voluminous and helpful) comments on this page, please?

  61. This is a sequel to Peter Earl’s post above of April 2013. I too changed what I think were the original batteries in the powertube of our ten year old Watchman Plus, but still got the ‘r’ and flashing red light every three seconds. On testing the powertube terminal there was virtually zero volts. So I drifted out the powertube terminal connection (it looks like a TV aerial socket) from the copper tube with a long rod and hammer. There was no current between the tiny pin and the positive terminal abutting the battery +ve. So I ground away the positive terminal which revealed a white hard substance, presumably the resistor mentioned by Peter. I carried on grinding away with a carborundum wheel, shortening the connection by about a centimetre until eventually a tiny central hole appeared. Into this hole I inserted a small brass gimp pin, clipped short, to make the contact between the connection’s central pin and the positive terminal of the battery. Then I reassembled, but needed a longer spring at the negative end because my grinding had lengthened the distance between my new positive terminal (the head of the gimp pin) and the copper tube cap. Final test – 6volts. Bingo! Hope this helps – I’m too old and technically incompetent to put it on u-tube.

    1. Thanks for detailing this. Your description made me wonder if it would be possible to hack the powertube to act as an antenna, but to wire power to an external battery pack – 433MHz AM transmitters that I’ve used have been generally tolerant of deviations from the designed antenna spec. Of course, the sensible solution here would be to replace the unit, but there’s little satisfaction in that.


    Was showing ” r ” and red flashing on plug in receiver.
    A combination of above and YouTube pointed to battery replacement in transmitter power antenna located inside oil tank. A few tips advised below might help someone………………..

    1] The power antenna simply screws off the ”aerial ” transmitter.
    2] On the other end is a cap which needs to be tapped off .
    3] It is NOT a screw thread so don’t use a spanner or ratchet to grip the end cap.
    4] It needs to be tapped off using something bigger than the tube and smaller than the cap.
    5] A number 16 ring spanner , WD40 , and lots of patience worked or me !
    6] Work within a confined space so not to lose the end cap and spring connection which will come off to reveal the batteries .
    7] New batteries [ 4 x AAA ] to be inserted positive side first.
    8] Spring connector back into cap pointed end connecting with batteries.
    9] Tap the cap back onto the antenna to original position .
    10 ] Screw the power antenna back on the aerial transmitter.

    Total cost = 4 x AAA batteries

  63. Thank you for writing this. It worked a treat. Took 5 minutes using an adjustable spanner snug around the stem of the power tube to provide a surface for a hammer to gently tap off the lid. The previous batteries had lasted 13 years.

    However, it took ages to find the correct transmitter hidden within my oil tank, the one with the power tube on top, as there are two – one for the tank and the other for the bund. Kingspan tried to flog me a new Sensor, but did help me locate the power tube. Reduce, Reuse, Recycle.

  64. Danke für die prima Hinweise zum Watchman!
    Ich wollte heute die Batterien nach Anweisung tauschen und gekam die Kappe nicht herunter.
    Mit einem Dremel und der dazu gehörigen dünnen Trennscheibe habe ich zwei gegenüberliegende Schlitze in die Kappe vorsichtig geschnitten. Danach kam man mit einem kleinen Schraubendreher vorsichtig die Schlitze leicht auseinander biegen.
    Dann geht die Kappe super leicht ab.
    Vor dem Zusammbau die Kappe wieder leicht zusammendrücken.
    [Translation to site’s language]
    Thanks for the great advice to Watchman! Today I wanted to change the batteries according to instructions and could not get the cap off.
    TIP: With a Dremel and the associated thin cutting disc, I have carefully cut two opposing slots in the cap. Then you use a small screwdriver to carefully ease the slots slightly apart.
    Then the cap goes off very easily. Lightly squeeze the cap again before reassembling.

    1. Thank you for sharing, that’s a great tip to release the tensions that may have seized the cap in place.
      Vielen Dank für das Teilen. Dies ist ein großartiger Tipp, um die Spannungen abzubauen, die die Kappe möglicherweise festgehalten haben.

  65. My Watchman was flashing ‘low bat’ and so following instructions on this site I have replaced the batteries. However after putting the transmitter back I’m still getting the same ‘low bat’ reading. Does anyone have any suggestions. I used brand new Duracell batteries, do they need to be specific batteries?

    1. The manufacturer fitted batteries are, from what I’ve read, exactly the same chemistry as retail. I would check that the battery terminals have good clean connections. Corrosion adds resistance, which results in a lower voltage, so scratch away at the internal terminal (e.g with a long flat-head screwdriver), and check the others too, just to make sure.

      Otherwise, I would ignore the warnings for now. It could be that the batteries are fine, but voltage measurement circuit is faulty. Or it might just be cold weather, which also causes battery voltage to drop.

    2. I am having the exact same problem as you. I have changed the batteries 3 times now. First time with energiser max plus and they lasted a day before telling me they were low. I took them out and tested each battery and the voltage went from 1.67v per battery down to 1.10v. I then cleaned and dried everything possible and changed for another set of energiser max plus. Again another day before the red light started flashing. This time I left it and a day or 2 later the unit then said ‘C’. So I then changed for another set of batteries, this time Energiser max with a voltage of 1.71v each. 2 days have passed and this morning I see the red light flashing again advising low battery.

      Did you figure yours out or can anyone else advise please? I’ve now spent £10 on batteries that are just getting eaten up in a matter of days with this thing

      1. If the voltage has fallen even on the second set of batteries, then maybe there’s a short-circuit somewhere in the wiring. If you have the sensor designed for a bunded tank, there’s the leak-detector (white spiky ball) that’s connected to the transmitter. I’d check that wiring first, perhaps disconnect it to see if the batteries last longer. Note that you will get ‘C’ if this is disconnected, but the readings will work regardless.

  66. I am not sure how to proceed. My Watchman Plus is flashing alternative readings (e.g. 6 and 2) after a power cut. I have switched off the system for 30 mins, and then restarted it with 2 separate power tubes, one of which is only a year or so old (like others, I found it impossible to prise off the tip of the rods, to insert new batteries.) Is a new monitor best or a general upgrade, and how easy is the latter to do yourself?

    1. Hi, unfortunately it sounds like it might have been fried after the power cut – I had exactly that happen to me, and I had to replace the receiver (I chose to do this rather than replace the whole thing with a Watchman Sonic). Just replace it – the new ones are easy enough to fit, so far as I’ve read. The only alternative is to find one second hand to replace both the transmitter and the receiver (they are locked together).

      For completeness, I’ll add that the RF signal is not encrypted. An Arduino microcontroller with a screen and an AM receiver module would be able to pick up and display the tank level. But that would just be for fun. For a much simpler life, just replace it!

  67. Many thanks for these comments. I had gotten round lately to thinking that perhaps a second-hand monitor/receiver might do the trick, but from what you say, if the transmitter and receiver are locked together, it doesn’t sound as if a the receiver on its own would suffice.

  68. this is fabulous information-
    I’m not overly technically minded-but I got the top off and in went the batteries-you’ve saved me between £29-70 for either the powerstick or a new set up.
    thanks so much,

  69. Thanks for this. Saved me £30 for a new power stick.
    Helpful hints
    1. When you knock the cap off do last bit inside a clear plastic bag and you won’t need to search on the floor for the small spring!
    2. Make sure you don’t get grease on the battery terminals and spring or you won’t get a connection (I made this mistake first time and red light/letter r continued to show)
    Thanks again

  70. Thank you very much for your advice. Just put four new AAA’s into the power tube, and we are up and running again. Amazing those batteries have lasted over 15 years, and now you have saved me the cost of a new power tube and probably a call-out charge, as I could not tell where the batteries needed to go!!!

    1. 15 years is pretty good going, particularly for alkaline batteries on low drain. The power-tubes were designed to be discarded, which reduced manufacturing costs. Not unreasonable, given the service life, but still avoidable waste with a little effort. Good work!

  71. Thanks to for your detailed instructions, I have managed to fix the issue that I had – dead batteries. We moved into our house in 2003 and the unit worked for almost 17 years. I used a jubilee clip as a collar to the cap and then slid an adjustable spanner along the battery tube to gently tap the clip, lubricated by powdered graphite. Another upcycling result!

  72. Yes, I found the tube batteries were replaceable. I can’t remember why but I later chaged to the Apollo ultrasonic oil level transmitter. I was changing that battery and dropped the transmitter into the outside part of the tank! Can’t get it out so just want a new transmitter without the receiver. Can’t find anywhere selling just the transmitter. They try to get you every which way!! 🙁

    1. The reason the transmitters aren’t sold separately is that they’re coded together with the receiver – it stops you receiving your neighbour’s oil tank level! Pairing devices is usually problematic, so I think it’s really just a convenience thing.

      You might still be able to rescue the transmitter – a bright torch, fishing rod, long stick or litter picker, and some steps to let you lean in a little. Maybe make a big hook from coat-hanger wire.

      Good luck!

  73. Hi,
    I’ve had a bunded tank with a Watchman Niveau for a couple of years. I bought it second hand.
    The level meter worked fine from installation, but then the batteries failed and I replaced them with AAA’s.
    It then worked fine for another year. Yesterday the reading suddenly changed to r.
    (Nothing has changed since installation and I’ve not had a power cut).
    I know this is an error message for no signal. I replaced the batteries, just in case it was them, and checked the ‘centre pin to copper case’ reading and I get 6.5V.
    I switched off the receiver and left it for a while, then I switched it back on and installed the power pack.
    After quite a few hours I’m still getting the r message.
    I’ve plugged the receiver into another socket only 2 meters from the tank and I’m still seeing the r.
    Is there any check I can make to find out what’s wrong please?
    Any advise gratefully received.
    Thank you.

    1. If you’re sure the wall-plug hadn’t been turned off, yet you see ‘r’, then I think the plug itself is faulty. If the transmitter had failed, then the wall plug would just continue to show the last reading with a flashing LED to warn you that no readings have been received for a while. So perhaps your transmitter is working fine.

      On the other hand, if the wall plug had actually been reset, but you were just unaware of it, then a faulty transmitter would likely be the cause.

      If you like enjoy electronics, it’s possible to get e.g. an Arduino to read the RF signal and decode it to a tank reading. Otherwise, your sensor probably just needs replaced.

  74. Hello all, I have a Watchman Niveau which has been running since 2006 and have only just replaced the batteries and now working fine again. However, I was then tempted to read the signal into Home Assistant and followed the instruction at https://community.home-assistant.io/t/oil-tank-level-monitor-watchman-sonic-rtl-433-integration-for-rf-sensors-or-level-sensors/223986

    I can pick up 4 or 5 SonicStd signal in the local area but not my Niveau! Does anyone know the frequency the Niveau is transmitting on and the protocol?

    Many thanks

    1. The Niveau uses OOK modulation, whereas the next generations use FM. It’s often possible to read OOK modulation with an FM module, but it’s a bit flakey. Given the price of an AM receiver, you’d be better to use that instead.

      Just hook up the module to a pin and sample the waveform. You should be able to figure out the data encoding without too much trouble. The transmitter can be made to send just by connecting the battery. I think it sends twice immediately, before entering its normal periodic transmit (15 minutes or so, as I recall).

  75. I have an old style watchman in a non Bunded tank. It’s worked fine for many years and has had the batteries replaced before.

    It stopped working with a flashing C after a fill up last week. I’ve investigated today and the batteries are good (I can hear the clicks when I connect the battery tube).
    I’ve also confirmed without the tube connected the receiver shows a r in the display.
    As soon as I connect the battery tube this changes to a C.

    I’ve removed the sensor from the tank with the depth gauge attached and as I lift the sensor out of the tank the display almost immediately reports a measure (eg 8 or 9). As I lower the sensor and depth gauge back into the tank the level display changes from 8 to 9 to F. Then as I put the sensor back fully on the tank the display changes to C.

    Could it be that the tank has too much oil ? Eg not enough depth for the echo to work ? I guess time will tell as the oil level drops ?

  76. Nice tip / instructions for changing the batteries. Hard to find this information for older style Watchmens. Thanks Kevin

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