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Old 03-02-2011, 09:18 PM   #1
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Furnace limit switch


Why does limit switch keep going on furnace? I need to buy a new one about once a year (last one was bought Feb 2010). This is Heil gas furnace and it is 19 years old. I've replaced about 1/2 dozen limit switches since I've had this furnace.


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Old 03-02-2011, 10:00 PM   #2
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Furnace limit switch


Most likely the duct is to small and the furnace overheats all the time. Limits only cycle on and off so many times before they break. A normal system never needs a new limit.

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Old 03-03-2011, 07:09 AM   #3
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Furnace limit switch


are you useing the o.e.m parts or aftermarket you can place a thermometer in the duct above the furnace to see what the temp is if it is going over the limit temp you have an air flow problem if not you have a itermitten short or power surge problem
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Old 03-03-2011, 11:52 AM   #4
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Furnace limit switch


Is this furnace limit control on the body of the furnace or is it a vent or spill limit control? Are you replacing them with limit controls that have the
same temp ratings as what the manufacture calls for? Is the limit control in a location that could be affected by a cracked heat exchanger?
Anything that restricts the airflow through the system can get it to trip.
A limit control that is tripping on a regular basis is showing you that the system is not operating properly. Having it trip so often that it is breaking says that this is serious and needs more immediate attention.
My last job where this was a consistant problem was tracked back to a factory fan motor running in the wrong direction.
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Old 03-03-2011, 11:59 AM   #5
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Furnace limit switch


Why blame the factory? Did they install it? In my book, a blower running in reverse sits with the installer not inspector #12 at the factory.
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Old 03-03-2011, 05:23 PM   #6
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Furnace limit switch


Blaming doesn't sort out the problem. The furnace just needs to be fixed.
My example was just to show how many different obscure causes can cause limit trips and how we really need more detailed info to try and address it.

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