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My gas furnace limit switch had to put in manual to get heat so I bought and installed a new one after a tech came and checked everything out so I installed the new resideo and it worked fine for two weeks and same thing happened I had to run it in manual so I’m on my second new one and its running fine for now so what is causing this to happen?

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  • welcome to Home Improvement, please take the tour. Then, edit to tell us what brand/model your furnace is and maybe a picture of where this limit switch is to ensure we're all talking about the same thing. Also, what is a "resideo"?
    – FreeMan
    Feb 10 at 15:57

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Limit switch can mean different things sometimes. Is it the limit switch that trips if the heat exchanger is getting too hot, or is it a limit switch in the burner area that serves as a roll out switch?

If it is the heat exchanger getting too hot, then you likely have an air flow problem. Either a blocked or partially blocked return or supply. That would keep the heat exchanger from effectively exchanging heat between the hot tubes and the supply air. I would check your air filter, and your A/C coil to see if either one appears plugged. Change filter if needed or clean the coil if needed. Also ensure that the blower motor is blowing air properly. If none of those are the issue, move out into the ductwork to see if there are any problems there.

Now if it is a roll out switch limit, that could be indicative of a more serious issue. Usually the only reason a roll out switch trips is because of a cracked heat exchanger. If it's the roll out, you need to have the HX inspected and make sure there are no cracks. If there are cracks, it could potentially leak carbon monoxide into your home whenever the heat is running. No fun.

You could also potentially be seeing symptoms of a clogged air intake or exhaust for the furnace. Birds and bees love building nests in the pipes that run outside the house. Check those for any possible obstructions as well and clear them if needed.

I hope these possible answers help you.

As a side note, can you clarify what you mean when you say "put the switch in manual"? You can't put a limit switch in any mode as they are only usually a snap disk that can be reset.

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  • some formatting might make this a lot more readable.
    – FreeMan
    Feb 10 at 15:55
  • I'm on my phone right now and it won't let me hit enter to make a new paragraph. lol Sorry. Feb 10 at 20:00

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