Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Auto-Reset Thermal Switch

mike85k Member Posts: 46
Recently my thermal switch has been tripping. It started when I had a chimney liner installed, and is even more frequent since I had glass block windows installed in my basement. I had the contractor that installed the liner come check everything out and they claim everything is good, and turned my gas pressure down.
Its not a big deal to go reset the switch, but it sure is annoying when it happens in the middle of the night and it gets cold before we realize. Is there a auto-reset switch available to replace this one? Or is there something else I should be doing/check?


  • pecmsg
    pecmsg Member Posts: 4,861
    edited May 2021
    The switch is probably doing its job Do NOT replace with Auto reset!

    So the liner was replaced and the gas pressure changed, was a new combustion analyses performed? Get your service provider to perform one and a complete check.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,852
    edited May 2021
    When I heard "Glass Block" I have visions of a leaky basement window (maybe even Jalousie windows) that let lots of combustion air into the basement (even when closed) getting replaces with an air-tight partition that let in light but no air. Add a bathroom exhaust fan or clothes dryer to that mix and your chimney changes from an exhaust vent for the heater to an air inlet for those powered exhaust devices. When that happens and your gas heat turns on, the exhaust has no place to go, and the spill switch trips. Job done! Lives saved! Manually reset the switch and live another day and maybe the exhaust vents will stay off long enough to heat up the house.

    You may need to add a dedicated combustion air vent to the boiler room. I agree with Jamie... Turn off the heater until you find the cause of the venting system failure.


    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    EBEBRATT-Ed Member Posts: 15,544
    Seems to me it is possible they undersized the liner and maybe a combustion air issue.

    If you can't get satisfaction and a combustion test from your contractor check "find a contractor" on this site and post your location. Someone may have a recommendation
  • mike85k
    mike85k Member Posts: 46
    Wow, interesting feedback everyone. Thank you. To add a little clarity to the story, I had the Chimney liner installed last Fall, there was no liner before and we were getting build up on the chimney mortar due to the exhaust gases escaping from there, prior to that we never had any issues with this. Shortly after that was installed this tripped and I had the HVAC guys out to look at it, I don't know if they did a full combustion analysis but they found that my gas pressure was way to high (I recall them saying it was at 10 when it should be 1.5?) which seemed odd to me, but they adjusted. Then we went months without having an issue with this switch. With that lower pressure my whole system behaved better, I had issues before with noisy vents and short cycling and that completely solved that and it works wonderfully now.

    Now just a few weeks ago we had glass block windows installed, yes the old windows were very leaky, dry rotted thin fragile glass. The first night that the heat ran with those new windows this switch tripped and the thermostat called for heat for a few hours without the boiler running, I reset the switch and all seemed ok. It hasn't tripped again, but since its warmed up it hasn't been running too much. There are no other fans or appliances hooked into this chimney, its only the boiler. I have no idea if its undersized, though I'm sure that's possible.

    We have a CO2 detector in the basement, wouldn't that go off if this was spewing exhaust gases into the house? Do I just need better air circulation around the boiler? Its in an open good sized basement.
  • mattmia2
    mattmia2 Member Posts: 9,670
    You would need a low level co monitor to see the type of spill that would trip a functioning spill switch. Listed co alarms only alarm after very high, sustained levels of co. Also if it is burning cleanly there may be very little co in the combustion products.

    There may be a combination of an issue with the new vent system not being designed to draft correctly and the glass block reducing the air available for draft.

    Have you called a professional that is skilled at combustion analysis and checking and correcting draft issues yet?
  • mike85k
    mike85k Member Posts: 46
    No not yet, I have other contractors here doing other work, and now since the heat really isn't needed I'm not treating it super urgent, but I will be doing that next.
  • neilc
    neilc Member Posts: 2,703
    it's not that there are no other fans or appliances on the lined chimney,
    it's that there may be bathroom or kitchen exhaust fans reversing the air flow , back down the lined chimney, due to sealing up the basement windows.
    as others have said, you likely need a make up air supply for the basement,
    and a knowledgeable mechanic to check this out,
    you're sucking exhaust back down the chimney, that's bad.
    known to beat dead horses
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,007
    The switch is a temperature sensing device, not a current tripping device.