Furnace fan comes on in hot weather


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Old 07-11-19, 02:55 PM
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Furnace fan comes on in hot weather

My home gas furnace is in the attic. This summer when the weather gets hot the furnace fan will come on and run for 4 or 5 minutes, then shut off. It might do this 3 or 4 times a day during very hot weather. It has never done this before and nothing has changed. I have an attic fan near the furnace and it is coming on and running normally.

Should I replace the limit switch?
 
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Old 07-11-19, 09:19 PM
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Welcome to the forums.

Which limit switch ?
An attic can get hot enough for the fan control to start the blower.
You'd need to know which limit switch to replace. Some are adjustable.

If it's just a furnace..... shut it off.
 
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Old 07-13-19, 05:15 PM
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It runs the AC too so can't just shut it off. I was assuming the limit switch in the combustion area. It is not adjustable.
Thanks Pete
 
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Old 07-13-19, 09:20 PM
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Make sure the vent is not clogged with a birds nest, especially if your furnace is old and has a pilot.
 
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Old 07-14-19, 06:46 AM
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Hi, sounds like the limit may be just doing itís job, what is the actual temp in the attic when the fan starts ?
Geo
 
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Old 07-14-19, 12:57 PM
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I should have mentioned in my first reply...... you should look into more cooler air in your attic.
If your attic gets hot enough to start the blower...... you are taxing the A/C system.
 
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Old 07-16-19, 03:02 PM
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We have very hot weather and the attic gets hot. There is an thermostatically controlled attic fan almost directly over the furnace and it is working. The furnace is 20 years old and has never before turned on before. I have not checked the flu for obstruction, but that does make sense as it would keep heat in the combustion area. I replaced the limit switch this morning and we'll see if that does the trick.
 
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Old 07-16-19, 03:35 PM
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It would not be a flue related issue.
 
 

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