On Christmas day my furnace pilot would not kick on and the blower just kept running on and on blowing out cold air. A furnace tech came out and looked at it. He said the Limit was bad and he replaced it. Now the landlord said she received the bill and the tech made a note that the reason the limit went bad is because of a dirty air filter. I find this hard to believe because I have regularly changed the filters. Additionally, he looked at the one I had in the furnace at the time, and said it didn't look bad or too dirty. So, my question is what can make a limit go bad in a furnace? Could thermostat malfunction have anything to do with it?

  • Well, unless the tech said you were the cause, they're simply stating the most likely cause absent any other good reason. It doesn't really mean it's your fault. The previous tenant perhaps didn't have the same maintenance schedule as you. Show your landlord the receipts for the filters. If that's not good enough, feel free to bug them every 4-6 mo.s to change it out for you. Commented Jan 17, 2015 at 9:17

1 Answer 1


Reduced intake air is the most common cause. This could be caused by a dirty filter, blocked/restricted returns, or any other restrictions of intake air.

The truth is, limit switches can only trip so many times before they break. Each time the furnace overheats and trips the limit; for whatever reason, the life of the switch is reduced.

It was likely not caused by a single trip. The problem will likely persist, if the root cause is not fixed.

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