Water heater not working? Water heater won't light? I'll show you how to troubleshoot and diagnose the problem with your water heater and Honeywell gas valve. I tested the igniter, the thermopile, the thermal switch and the pilot valve and the main burner valve on the Honeywell gas valve, and all were in working order. The problem was the Honeywell gas valve control board had failed. I replaced the control board, and fixed my water heater.

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NOTE: Before purchasing a part, confirm the part works on your water heater model.
Honeywell Gas Valve WV8840C1406: https://amzn.to/3GNlCtF
eBay is a good source to find pre-owned and new Honeywell control boards and gas valves.
Reliance Water Heater 9007876 Gas Thermopile Assembly: https://amzn.to/3cXANCq
(If you have a Reliance water heater and need a thermopile, it's cheaper to purchase the entire pilot assembly, which includes the thermopile, pilot and igniter, on Amazon than it is to purchase the thermopile alone. The assembly includes the pilot tube.)
I used a Harbor Freight 7 Function Digital Multimeter. It's about $7.00 at Harbor Freight.
Dollar Tree has 9 volt batteries for a dollar.

How to test a water heater igniter
How to test a water heater thermopile
How to test a water heater thermal switch
How to test a water heater gas valve
How to test a water heater pilot valve
How to test a water heater main burner valve

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