Gas water heater pilot goes out after heating

Discussion in 'Water Heater Forum, Tanks' started by EDM, Feb 13, 2019.

  1. EDM

    EDM New Member

    Joined:
    Feb 13, 2019
    Location:
    Boston, MA
    Recently our gas water heater pilot has been going out after the burner has heated
    the water. The interesting thing is that it does not seem to be possible to relight the
    pilot for a while afterward, when depressing the button to light it in the PILOT position,
    it will light but goes out slowly as the button is released. However, later, it will light
    and stay on.

    Have replaced the thermocouple but that does not seem to have made a difference.
    Will try cleaning the pilot orifice, but am I correct in assuming it is probably the gas valve?

    The pilot flame is fairly large but I do hear a sputtering noise.
    I do not think based on observation that there is low gas pressure in the house.

    Thanks.
     
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    Is the thermocouple properly positioned in the pilot flame?
     
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  4. EDM

    EDM New Member

    Joined:
    Feb 13, 2019
    Location:
    Boston, MA
    I believe so. It certainly was for 15 years before it started acting up.
    After replacing the thermocouple the pilot will stay on after being initially lit.
    It is only after the burner has been on heating the tank that it goes out
    and, for a while, after relighting won't stay lit. Then it will work OK.

    I think the new thermocouple is in the correct position in the pilot flame,
    about 1/4" to 1/2" of the end is in it.
     
  5. plumber69

    plumber69 In the Trades

    Joined:
    Jun 20, 2014
    Location:
    Prince Rupert, British Columbia
    Is there a high limit reset on the tank?. It could be a manual red button or one that resets it self.
     
  6. EDM

    EDM New Member

    Joined:
    Feb 13, 2019
    Location:
    Boston, MA
    I looked, but I don't see any kind of reset. The valve is a RobertShaw R110RTSP 66-178-335.

    Was able to test the old thermocouple held in the flame of the gas stove, it read 35mV.
     
  7. plumber69

    plumber69 In the Trades

    Joined:
    Jun 20, 2014
    Location:
    Prince Rupert, British Columbia
    might look like this. Its not on the gas valve. below it
     

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  8. EDM

    EDM New Member

    Joined:
    Feb 13, 2019
    Location:
    Boston, MA
    No, there does not appear to be any kind of limit reset.

    It does seem like the pilot will only stay lit after enough time has passed since the
    main burner has been on (or, maybe, after the tank has cooled down). It does not
    reach the same hot water temperature that it used to despite being on the highest
    temperature setting when it is heating.
     
  9. plumber69

    plumber69 In the Trades

    Joined:
    Jun 20, 2014
    Location:
    Prince Rupert, British Columbia
    Ive had gas tanks that would only leak inside when heated up. Then would drip and put the pilot out
     
  10. EDM

    EDM New Member

    Joined:
    Feb 13, 2019
    Location:
    Boston, MA
    Replacing the gas valve/thermostat fixed the problem. I suspect that the solenoid
    was faulty, and would stay open for a while, but not continuously even though the
    thermocouple voltage was OK.

    Appreciate all of the advice/suggestions. Will end up replacing the tank eventually
    given the age but needed to get it back operational. Checked carefully - no leaks.
     
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