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  1. #1
    Join Date
    Mar 2009
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    238

    Default Gas Heater Pilot Keeps Going Out

    The thermocouple was just replaced on my gas fed house heater and its been fine for the past few weeks. Within the past hour the pilot blew out twice. Any ideas?
    My advice and opinions come from hands on knowledge...and This Old House Hidden Content

  2. #2
    Join Date
    Jul 2010
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    SoCal
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    Default Re: Gas Heater Pilot Keeps Going Out

    In the past 2 weeks I already had 4 calls similar to your situation for 3 furnaces and 1 water heater.

    The water heater and one furnace had bad thermocouples and are working fine now.

    Another furnace had a bad gas valve/thermostat combo. Replaced the gas valve and it's fine now.

    The last furnace was just too old (31 years). Replaced the furnace and the new one is working like a Boeing 737.

    With the limited information you give, I tend to think it's the gas valve, it could be the gas supply to the pilot.

    Another source of gas supply interruption is spider webs in the line, in which case a line cleaning will help.

  3. #3
    Join Date
    Mar 2009
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    238

    Default Re: Gas Heater Pilot Keeps Going Out

    The boiler is a Weil McLain 9 series installed around 1990 i assume because its the oldest documentation i can find on its maintenance. I just had the thermocouple replaced a few weeks ago. I had to relight it 2 more times since this post but now it wont stay lit at all. I get a nice blue flame when set on pilot but after several tries of holding the pilot button down to let the thermocouple heat up, it still doesnt stay lit. Could it be the gas control assembly or is a brand new thermocouple dead? Any way i can check?
    Last edited by dcalabro; 12-05-2011 at 08:33 AM.
    My advice and opinions come from hands on knowledge...and This Old House Hidden Content

  4. #4
    Join Date
    Jul 2010
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    SoCal
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    Default Re: Gas Heater Pilot Keeps Going Out

    There is always the possibility that the 'new' thermocouple you just installed is bad, though remote. If you want, replace it and see if it holds the flame.

    If it doesn't, move on to the gas valve (control). Caution: changing the gas valve is a job for a qualified experienced tech only, not for an inexperienced DIY.

  5. #5
    Join Date
    Mar 2009
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    238

    Default Re: Gas Heater Pilot Keeps Going Out

    A friend replaced the thermocouple, and it fired up fine....for an hour. i re-lit it, then it worked fine again...and later went out. I tried to relight it for a 2nd time and no luck. It wouldn't hold the flame. I then realized that under the thermocouple assembly there was also a orange flame in addition to the normal blue pilot flame at the top of the thermocouple so I knew something wasn't right.

    I turned the unit to Off, took the burners out to access the thermocouple assembly and sure enough the gas line that feeds the pilot within this same assembly was loose. When trying to light the pilot, this escaping gas was lit and apparently not letting the pilot receive enough gas to hold a steady flame. That or the gas control unit sensed that more gas was being used than is required for a pilot to burn(just a guess but i'm not even sure if a pilot gas valve can do this.)

    Also both with the old and new thermocouple I noticed that it was a little crooked and the right side of the pilot would lean against one of the burner tubes so I also straightened this so the pilot flame doesnt directly touch the burner tube anymore.(simply loosening the screw for the thermocouple bracket and moving it over 1/8 inch. I didnt bend or twist any metal so no worries)

    Bottom line is that it held a flame throughout the night it burns cleanly and a steady blue like it should on a gas pilot.
    My advice and opinions come from hands on knowledge...and This Old House Hidden Content

  6. #6
    Join Date
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    Default Re: Gas Heater Pilot Keeps Going Out

    Terrific! job well done.

  7. #7
    Join Date
    Mar 2009
    Posts
    238

    Default Re: Gas Heater Pilot Keeps Going Out

    Unfortunately, the problem is back, kind of! For the past few weeks as cold weather has moved in, the pilot again goes out and is easy to relight this time. The only solution seems to be if I leave a basement window cracked open, the pilot is fine! I've tested this over many days of trial and error, leaving the window open and closed and it is a clear pattern. The basement door has a good 1-1/2 inch gap under it to allow air to flow to and from the first floor so I can't imagine that the basement is losing all of its airflow.

    Another thought its that maybe with the colder air, the temperature change of the chimney is changing the amount/speed of air flowing up. I know I have not yet put a cap on the old brick chimney but i'm curious if this would definitely solve the problem or if there is something else going on.

    Worst case, I have to leave the window cracked for the winter, making the direct floor above it colder and increasing my already high gas bill.
    My advice and opinions come from hands on knowledge...and This Old House Hidden Content

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