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Thread: Pilot light went out, won't stay lit

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    DIY Junior Member speedtrpl's Avatar
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    Default Pilot light went out, won't stay lit

    Rheem Model # 21V40-7
    40gal
    SN 0793134209

    The pilot light went out yesterday. I assumed it was the thermocouple. Replaced it today. I can re-light the pilot and it stays lit. The gas come on and heats up the water to desired temperature, but then when the burner goes off the pilot goes out.

    HELP!

  2. #2
    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    Quote Originally Posted by speedtrpl View Post
    Rheem Model # 21V40-7
    40gal
    SN 0793134209

    The pilot light went out yesterday. I assumed it was the thermocouple. Replaced it today. I can re-light the pilot and it stays lit. The gas come on and heats up the water to desired temperature, but then when the burner goes off the pilot goes out.

    HELP!
    Could be a faulty gas valve....

  3. #3
    DIY Junior Member speedtrpl's Avatar
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    Thanks...I will try that now....here's more updated info:

    When I first light the pilot and then manually rotate the temperature dial back and forth and the burner cycles on and off, it is not pulling the flame away from the thermocouple. The pilot stays lit. It only seems to go off after the burner completes a full cycle and the water reaches the desired "full" temperature and shuts down on its own.

    Then the pilot light will not stay lit until the thermocouple cools down again. This seems really strange to me. I put it back on Pilot setting and hold the button down and put a match to it and it flames as long as the button is down. As soon as I release the button it goes out. After everything cools, I do it again and it will stay lit on it's own. I watched it stay lit in Pilot mode for an hour.

    I believe the pilot line is fine because it works when everything is cool. It just seems to stop working after it goes thru one complete cycle on it's own. Why can't I immediately re-light the pilot if it's already hot? Is this a feature of a thermocouple?

    Suggestions?
    Last edited by speedtrpl; 03-13-2010 at 06:39 AM.

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    Master Plumber Redwood's Avatar
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    What brand and model is this water heater?

  5. #5
    Moderator & Master Plumber hj's Avatar
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    Thermocouples are "heat sensitive". If the flame is not applied to the correct portion of it, or the entire thermocouple gets hot it will not generate the power needed to operate the gas valve. But normally, that means that if the burner's flame is enveloping the thermocouple, that it would shut down before the water reached its temperature setting. But, for all we know, that could be what is happening. If so, check the heater flue and chimney for poor draft or blockage.

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