My hot water heater stopped working, after testing the pilot light, thermopile, thermoswitch, pilot valve and main burner valve—all which are working well—I came to the conclusion that the board was dead.

I have a WV8840B1117 (2013 board) Honeywell valve controller. I managed to scavenge 3 boards off some tanks out at the dump (older ones - WV8840B1000 - 2009 boards), but none of them worked (no status lights, no valve action). I ended up calling a gas company, and they had a used valve off of a tank that sprung a leak (WV8840B1051) they sold me for $20. This controller at least had some life in it. When I tested it with an AA battery I could get the pilot valve to open, and the status light started blinking, and if I was quick enough and turned up the heat I could hear the Main burner valve open, but it would only stay on for a couple seconds before it started giving me the "low thermopile voltage" warning and shut off. Operating voltage is supposed to be 650-850 millivolts, and the battery puts out 1,500 millivolts, so if anything it has TOO MUCH power, not to little. I hoped it would still work under normal voltage, but when I installed the card in the valve on the tank I could get it to do anything with the 900 millivolts from the thermopile, but I could get the burner to fire up on battery, but again only for a few seconds before it died.

There is a chance that I could have just gotten ANOTHER bad board, but I've gone through enough now to start wondering if something else might be going on.

Is there a reason my board would indicate "low voltage" when it's receiving high voltage other than the board is fried?

  • How old is the tank, did it have a warranty? It is possible your best bet is to replace it.
    – Gil
    Jan 9, 2023 at 23:12
  • The gas valve and the control board have to be matched
    – Traveler
    Jan 9, 2023 at 23:52
  • Why are you fixated on the control board? Might be a stuck valve or a weak thermopile. Jan 10, 2023 at 7:21
  • @Harper-ReinstateMonica As I mentioned in the question: I tested the valves, all working, and the thermopile is putting out <900mv. Everything else appears to be working well.
    – ShemSeger
    Jan 10, 2023 at 20:31
  • @Gil The tank is about 1 year past its warranty, but the tank is still in perfect condition. As a matter of principle I'd rather fix something than throw it away.
    – ShemSeger
    Jan 10, 2023 at 20:42

1 Answer 1


Voltage is one thing, current is another. A double A battery can only supply so much current at a time, probably not enough to operate the valve properly even though the specs only call for about 3/4 volts. Isn't the board normally powered by a transformer? Have you checked that for correct voltage and amperage? Also, are you sure the board / valves are expecting DC current (as a battery supplies) and not A/C out of a transformer?

  • 4
    The amount of current you can get out of a AA is far more than a thermopile.
    – user71659
    Jan 10, 2023 at 0:00
  • Power to the board is provided by the thermopile, it only needs about 650-850mv for normal operation.
    – ShemSeger
    Jan 10, 2023 at 20:33
  • I guess I didn't know what a "thermopile" is ....it sounds like something my dog does every morning on her walk. ,..,..sorry couldn't resist! As the Borg would say "resistance in futile" and i say resistance is not futile if you have at least 100,000 ohms! please don't snip me on this,....just having some fun. Jan 11, 2023 at 1:34

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