Eratic function I have An AO Smith Model FPSH 40-260 Nat gas water heater. when I turn it on it heats water up the first time. then when it calls for heat again, fan comes on - glo plug starts -gas does not come on - glo plug shuts down - fan shuts down. and it keeps repeating this cycle until I turn the switch off. after a couple days I can repeat this and it will do the same thing. Is this maybe the control valve? Doug

It is the control valve - however not in the sense that IT is bad - the thermocouple on your unit is bad.

The purpose of the thermocouple is to convert the heat from the pilot to a miniscule amount of energy that the control valve senses letting it know the pilot is present... a default safety so gas does not fill the house!

With no pilot (which you have) or no SIGNAL to the control valve, it will not open to allow the burners fuel for ignition.

Sometimes the thermocouple is out of position (should be at the tip of the pilot light)...

Sometimes it is covered in soot, and can be cleaned with a fine sandpaper...

Sometimes it needs to be replaced altogether.

Most thermocouples are generic, but some are a specific value. Check with your manufacturer for a part #.

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