Furnace Thermal Cutoff With Hanging Downward "Wheel", Or ?


Moved into a 30 yr old house with a forced gas hot air heating system.

Saw something near the furnace wiring which I'm not familiar with.

Seems like they have a regular 4 inch square type gang box mounted in very close proximity to the furnace with what looks like a threaded rod/stud hanging downward from, with a round wheel on the hanging stud.

Is this a thermal safety shutoff ?

Who manufacturers them, and what are they "officially" called or termed ?

If so, how does it work; is it likely for the 110 V power feeding the furnace ?

Would there be any possibility that if this is the purpose, they might have it wired into the chained together smoke detectors for an indication if it is ever tripped ? Did they ever do this type of scheme with smoke detectors way back, possibly ?

Or,... ?

Thanks, Bob

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Descriptions suck rocks

Pictures please and then maybe we can help ya.

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I have something similar. The wheel has 6 holes in it? Mine reads something like "Firomatic Thermal Cutout" and I think there is a temperature on it somewhere.


Firomatic, I guess. Thermal cutout.

Mine just cuts off 120V power if activated. I suspect it is a one-shot device.

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Michael Moroney

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