JOHN F wrote:
I have a forced hot air system and I have had to replace the limit switch 4
times in last 11 months. Part number HH 12zB and it has 200 degree rating.
All power feeds measure correctly. This is in town house with 3 floors of
ductwork. System works fine between limit switch replacements. I have
lined out limit switch for short durations ( middle of night and heat
needed), but I consider this a fire hazard over long term, plus unit runs
continually in that mode. With defective limit switch, fan runs
continuously when themostat calls for heat, but naturally the unit doesn't
actuate the pilot, so get cold air only.

Parts are fairly cheap..like less than $10, but more an irritation and
concern when traveling.

Thanks

The "limit" part of a limit switch is a safety device which should never
be exercised in a proper installation, because the furnace should never
reach the temperature to which the limit switch is set.

If yours is activating, you have another problem. As others have
suggested, it could be a fan set to the wrong speed, an incorrect
limit temperature, a clogged filter, and/or incorrectly sized (or
blocked) ducts.

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