Gas water heater burner on, pilot off

[Tesisat Ankara]

The pilot lights as long as the dial is pushed in, but goes out when the dial is turned to ON.

However, once the thermocouple is heated (by the pilot being held on) gas turns on in the main burner. It doesn’t light because the pilot has already gone out. If I hold a match to the main burner at this point, it lights and stays on until the tank water reaches the temperature set.

The pilot is off all the time the main burner is on and doesn’t relight unless the dial is turned back to “pilot” and depressed.

The water heater is Hoyt (pre-1970)and the thermostat is Unitrol.

Pilot flame is bifurcated, one jet aimed toward main burner and the other jet aimed toward the thermocouple tip. It looks a healthy blue and strong.

Any ideas?

[SelgasParticipant]

Sure sounds like you have one of two things faulty there my friend, firstly I would suspect the thermocouple lead itself as being on it’s way out (failing), secondly it could be the main Unitrol valve ECO device that has failed, however if the latter is the case this fault is usally identified by the main burner lighting up as normal once the pilot is relight then once the water temperture as reached the set temperature it shuts off the main burner and also trips the safety device and shuts down the pilot as well, which will not relight until the temperaure of the water has dropped considerably below that of the set temperature. You may also wish to check the actual pilot burner is in fact playing directly onto the thermocouple lead – if not the thermocouple lead will not heat sufficently to operate the safety valve properly.

[[email protected]Participant]

We’ve changed the thermocouple twice now without affecting the problem, so it seems likely to be something else. The pilot flame hits the tip and heats it well enough to fool the safety device into thinking the pilot is still on, then, once the main burner lights, it keeps the thermocouple hot enough to disarm the safety device while the water tank heats. That’s what makes me think the thermocouple is operating properly. Is there a flaw in that logic?

Is the next step to change out the thermostat?

Thanks for your thoughtful suggestions.

[SelgasParticipant]

Yep you are on the right track.

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