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CG Boiler - Pilot Goes Out After Heating Cycle

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jinx1832
jinx1832 Member Posts: 7
Hello,

I have a Weil McLain CG Boiler that is acting up. The pilot goes out about 3-5 seconds after the heating cycle ends. I replaced the thermocouple and thermal fuse, but it is still shutting off at the same time. I am assuming excessive heat is triggering the fuse, but I am not sure why it would happen the same time after the heating cycle ends. Could it be a different electrical issue? Any help troubleshooting would be appreciated.

Thanks,

Josh

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  • JohnNY
    JohnNY Member Posts: 3,244
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    Is this a spark ignition with a ceramic pilot? Hairline cracks open up when heated. Tough problem to trace.
    Contact John "JohnNY" Cataneo, NYC Master Plumber, Lic 1784
    Consulting & Troubleshooting
    Heating in NYC or NJ.
    Classes
  • jinx1832
    jinx1832 Member Posts: 7
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    It is a standing pilot, it always hits the max set temp and then the pilot shuts off a few seconds latter. I tried to lower the max boiler temp and cycle time and it has the same result.
  • jinx1832
    jinx1832 Member Posts: 7
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    I should add the only way to keep the pilot on after the cycle is when you move the heat shield with the thermal fuse farther from the flames. This seems to point to a thermal issue, but the timing just seems odd.
  • JUGHNE
    JUGHNE Member Posts: 11,108
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    Is the thermal fuse a one time device?

    IIRC 1/3 of the end of the thermocouple should be in the pilot flame.

    Another thought is that after the main burner shuts off the gas regulator shuts down to far and pressure is lost to the pilot.
  • jinx1832
    jinx1832 Member Posts: 7
    edited November 2016
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    The pilot flame placement looks good. It is a Microtemp Thermal Fuse, I am able to relight the pilot and run the burner.

    I also tried to keep the power damper open after the cycle to see if it was a ventilation issue.

    When I run the cycle with the heat shield and thermal fuse in the vertical position, the pilot shuts of 5 seconds after it reaches temp.

    When I run it with the horizontal position, the pilot stays lit.






  • JUGHNE
    JUGHNE Member Posts: 11,108
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    Possibly the placement of the shield affects the draft in the burner chamber. With it up in the proper place the draft would possibly lift the flame and snuff it out when the burner shut down.
    Also not impossible is that when the main burner lights it snuffs out the pilot but the main burner is then heating the t-couple.

    You say the pilot goes out a few seconds after the burner shuts off....do you see it go out or do you hear the snap of the T-couple dropping out?

    IIWM I would check the gas pressure at the boiler during operation and shut down......is this Natural gas or LPG?
  • jinx1832
    jinx1832 Member Posts: 7
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    It is a Nat Gas system, there is definately a snap when the pilot goes out. I already replaced the T-couple, perhaps I should adjust it? Would the Thermal Fuse snap the same way?
  • JUGHNE
    JUGHNE Member Posts: 11,108
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    I believe your thermal fuse is just that, a fuse that when over heated will open. It is not repairable or resettable and must be replaced. One shot and you're done.

    The T-couple when heated produces a small electric current that energizes a magnet inside the gas valve to hold open certain passages allowing the gas to flow. The connection to the valve must be clean and secure. I use a pencil eraser to clean the button on the end of the T-couple where it screws into the valve.
    IT must be tight but too much muscle and will strip the opening.
    Just where it feels tight.

    I feel you might have a gas pressure issue and should consider calling a pro to check that out. FWIW
  • neilc
    neilc Member Posts: 2,716
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    as jughne suggests,
    sounds like a draft or pressures issue,
    while I'm gonna ask for a pic of the vent from the boiler to the chimney,
    I'm really thinking this is beyond homeowner tinkering,
    and should be seen by a burner pro
    known to beat dead horses
  • jinx1832
    jinx1832 Member Posts: 7
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    Appreciate the feedback, guys. Attached is a pic of the vent.

    I actually already had a pro at the house twice, he seems baffled. Perhaps, I should call somebody else.....



  • neilc
    neilc Member Posts: 2,716
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    known to beat dead horses
  • JUGHNE
    JUGHNE Member Posts: 11,108
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    Sometimes a NG company will check your delivery pressure at no cost. It is liability issues that prompts them to do this, (and they might be nice people anyway). If they or someone could check the pressure right at the boiler as it cycles on and off that would narrow down the pressure question.
    Do you have a NG water heater also?

    We appreciate feedback on your results, Thank You.
  • jinx1832
    jinx1832 Member Posts: 7
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    Yes, the water heater is NG. Would the pressure issue impact that unit as well?

    I live in Hampton, NH. I'll check the contractor listing.


  • JUGHNE
    JUGHNE Member Posts: 11,108
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    Sometimes delivery pressures will affect standing pilot lights of all appliances, sometimes, but not always.
  • STEAM DOCTOR
    STEAM DOCTOR Member Posts: 2,041
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    The thermal fuse(flame rollout switch) has nothing to do with anything. It only controls the main burner, not the pilot.
  • kcopp
    kcopp Member Posts: 4,448
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    I just had a couple issues w/ this exact same make/ model. Pilot would not stay lit. I changed out T-couple.... Same issue. Swapped out the gas valve all good.
    Fwiw... I am in Dover.
  • cass1983
    cass1983 Member Posts: 0
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    Was this ever resolved why the boiler pilot light was going out after the boiler reached its temperature and shut down both the burner and pilot light? I have exact boiler and it is doing the same thing even after I had a new valve installed because pilot would not stay lit. Pilot stays lit now no problem, just goes out after boiler reaches temperature and shuts burner and pilot down. thanks Marc