Water Heaters - Intermittent problems: gas HWH fails to stay on sometimes

We have a 25 month old A.O. Smith PowerShot. Works nicely. Most of the time.

We notice that after periods of heavy use, such as filling up the bathtub, we notice that there is no hot water. Upon checking the heater, we see the LEDs on the front indicate "System in Lockout" (according to the manual).

The manual gives three possible reasons: 1) Gas supply is too low, 2) hot surface ignitor not positioned correctly, 3) Low voltage to the water heater, and 4) electric polarity to unit is incorrect.

Did I say three reasons? I meant four.

We can powercycle the unit to clear the lockout state, and sometimes it fixes itself, but usually it starts and stops, starts and stops again, then goes back into lockout.

When it gets into this state, it takes a few hours for it to recover, and everything is fine..

The fact that it gets better after a few hours makes me suspicious:

1) Does this have something to do with the pressure in the municipal supply lines (it always happens around "bath time" at night)?

2) Or is there something that needs to "cool down" in there, like the hot surface ignitor that trips some kind of safety sensor?

I am at my wits end, and tired of having to wait till 1 am to take a shower on nights when we have run the dishwasher :)

Any help will be GREATLY appreciated.

Aaron,
I am about useless when it comes to this kind of stuff BUT I can google better than most.

I found a line in a Maytag manual dealing with the same lockout code that attributed polarity issue or a faulty ground. I have 2 LP water heaters in series. The first heats the cold water and the second acts a reserve. (We like lots of hot water) The first one was having the lockout issue.

I checked the little green ground wire and it was contacting the cold water inlet pipe. There was some corrosion on the big nut connecting the inlet to the tank. Some of that corrosion got on the ground's insulation. The wire was compromised just enough to create a problem. I taped the bare spot and so far it works like a champ. Now I gotta figure out why the nut is corroding.

Best of luck! Hope you get it fixed!

Thank. Yes, ground was a possibility, but flame sensing was the real culprit.

I apparently fixed it by cleaning the flame sensor with some steel wool, and maybe bending it a little toward the flame it was supposed to be detecting :)