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Pilot goes out on shut down

Pat_11 Member Posts: 49
20 year old gas boiler. pilot goes out on shut down. pilot appears strong, tried new thermal couple. Any ideas?
Thanks Pat


  • Terry St.James_2
    Terry St.James_2 Member Posts: 102
    Could be a few things there ........

    First I would change the thermocouple or thermopile
    if still not working...pilot burner might be clogged up....is the gas pressure good(it might be low pressure)you also might have a short or loose connection at the the powerpile or the power unit(could just be dirty too)
    Also if you have already changed the thermopile/couple...is it in the right place?
    One more thing ...pilotsat might be bad too....listed a few things there that might be of some help....hope it did .
  • Wes
    Wes Member Posts: 6

    I agree with all of the above. You might also want to make sure that there is no "draft" or "breeze" around the pilot that could blow it out. If there is you will have to fabricate a pilot shield.

  • could be flue gases condensing how dose the smoke pipe look rusted or white ash on the joints. What was said above should be checked first. Also do all the burners light off nicely or is there a bang or a whoff. You may want to have it cleaned and make sure the pilot assy and orfice is cleaned.
  • Dale
    Dale Member Posts: 1,317
    Shut down?

    I take that to mean when the thermostat is turned down to end power to the gas valve which shuts off the main burners. If the pilot only goes out when the call for heat ends and if the pilot flame if on 3/8 to 1/2 inch of the tcouple tip then the pilot gas is either being restricted or the pilot flame blown out. Sometimes a dirty orifice or incorrect main burner pressure will give an extinction pop that will blow out a pilot. Cleaning the main burner and orifices can't hurt.
  • Pilot outage

    Since you have replaced the thermocouple we can pretty safely assume it is something else. Make sure the flame is hitting the upper 1/2 to 3/8 of the thermocuple. The flame should be a soft blue flame. If it is yellow it is dirty and needs cleaned. I assume this is the first time this has happened in 20 years.

    If you have a multi meter with a DC scale on it you can take some millivolt readings. If you are interested in how to do that go to www.HVACTC.com click service and look for the best of "Tim McElwain" there is a video on checking millivolts on thermocouples.

    You could also be having combustion problems in the boiler room. Do you have sufficient air for combustion? Is the room a confined space if so it may need air from outdoors.

    How is the draft on the chimney? A simple test is to bring on all the exhaust fans in the house and the dryer. Close the damper on the fireplace. Then bring on all the gas equipment in the house, then take a match and go to the draft hoods of the appliances and see if you have the flame being sucked up into the draft hood. If it is blowing back you have a negative pressure condition in the house caused by mechanical exhausting.

    There could also be a gas pressure problem. Pilots are not regulated they are on line pressure. The inlet gas pressure to equipment should be somewhere between 6" to 10" Water Column pressure. this can be measured with a "manometer" (u-gauge) or a magnehelic gauge.

    It depends on your location but recently we have had some very strong winds in some parts of the country. This could also cause a pilot to go out.

    You say the pilot goes out when the burner shuts off. This may indicate a combustion problem caused by any number of things. When was the last time the burners were serviced? Are the boiler sections clean? When the burner shuts off does it make any noises or concussion sounds?

    These are a few of the things to look for. Let us know how you make out. If you are not a professional I would suggest getting hold of someone to check it out.
  • also saw the same senario when

    the incoming underground gas main got water inside it from a leak...main burner would work cause of its heavy demand, but the pilot wouldn;t stay lit...an upstream manometer test will give you quite an illustrative view of this if its the case..manometer water bounces around...just something else for you to add to the list.
  • Frank_15
    Frank_15 Member Posts: 33
    change the gas valve

    replace tha gas valve
  • Terry St.James_2
    Terry St.James_2 Member Posts: 102
    Thanks Tim................................

    We have had many windy days here too in Montreal. Never thought to consider that as a problem with the pilot. I did know that air sources have related to the outage. Hmmmm,must consider that now...had a few calls about pilots keep going out....thanks
  • Pat_11
    Pat_11 Member Posts: 49

    Thanks guys. I'm thinking dirty pilot orifice or gas pressure issue. I'll check them out. Thanks fo all your help. I'll let you know what I find.
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