High Limit Switch Tripping

Feb 28, 2023
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United States
My gas furnace high limit switch trips during every heat cycle. Is this normal operation? I am inclined to think that the furnace essentially overheating during every heat cycle is not a good or normal thing (possibly even a safety issue?).

I discovered this after replacing an old battery operated thermostat with a new wired smart thermostat. I noticed that the new wired thermostat would randomly lose power and restart numerous times a day. I soon learned that this was happening during every heat cycle when the furnace high limit switch would trip.

First remedy I tried was replacing the air filter. Limit switch still tripping. I ran 1 heat cycle without the air filter installed - limit switch did not trip. Fair to say I have an airflow issue at the filter??


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