I have a maybe 9 year old AO Smith water heater, model number FGR 50 242. The pilot is burning, but the burner will not light. I cranked the temp up all the way and nothing. I scrubbed the thermocouple (ie the device that sticks into the pilot light) lightly with a wire brush (just for fun I guess, I'm not sure what it might have accomplished since I think the thermocouple is ok) and nothing changed.

My guess is that the gas valve is no good?

I have replaced a good number of thermocouples over the years (not this unit) and if I recall the idea is that the pilot light serves a dual purpose - it lights the burner when gas is allowed to get to the burner; and via the thermocouple it heats, signals the gas valve a signal that it's on and it's OK to send major gas to the burner. The common issue where the pilot light won't stay lit can often be solved by replacing the thermocouple. When the thermocouple fails, all the gas valve knows is that the thermocouple is not sending a "pilot light is burning ok" signal any more, and it won't send gas to the burner. The gas valve also stops sending gas to the pilot light. At least I think that's the idea.

So if the pilot is burning, it means that the gas valve is getting a signal that it's safe to send gas, I would think. Since it's not sending the gas in this case, it's the soleniod in the gas valve? Or could this somehow be a thermocouple issue?

I am guessing that I can replace it. I have done a good deal of plumbing. But will the part be available to a homeowner at Home Depot or Lowe's, or is it a part only available at a plumbing supply house?

Thanks in advance - you guys helped me a lot with a gas furnace issue a couple of years ago.

Replaced the control valve and it works fine now.

Thanks for the update Whittle, were the parts easy to find?

Yes, I was able to get a like kind part from a local supplier on Saturday. It's not an AO Smith part but other than the length of the 3/4" connection to the water tank, was virtually identical.

I had a great thrill when I disconnected the control valve. A guy I'd talked to on the phone had said the 3/4" was not connected to the water inside the tank - it was just a mechanical fixing point, not related to water flow. So I took it off with the tank full and the cold water supply on. Surprise! Lucky I was able to get it back on before creating too big of a flood.

How do you remove the valve from the body of the tank?