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.
- Unscrew the power tube from your transmitter.
- 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.
- 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).
- Put the new batteries in, positive-end first. The negative end of the last battery will connect to the cap when you replace it.
- 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!