Furnace fan comes on in hot weather

Reply

  #1  
Old 07-11-19, 02:55 PM
Member
Thread Starter
Join Date: Jul 2019
Location: United States
Posts: 3
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?
 
Sponsored Links
  #2  
Old 07-11-19, 09:19 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 51,366
Upvotes Received: 206
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.
 
  #3  
Old 07-13-19, 05:15 PM
Member
Thread Starter
Join Date: Jul 2019
Location: United States
Posts: 3
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
 
  #4  
Old 07-13-19, 09:20 PM
Member
Join Date: Jul 2006
Location: Euclid, Oh
Posts: 340
Make sure the vent is not clogged with a birds nest, especially if your furnace is old and has a pilot.
 
  #5  
Old 07-14-19, 06:46 AM
Geochurchi's Avatar
Member
Join Date: Nov 2012
Location: USA
Posts: 3,835
Upvotes Received: 8
Hi, sounds like the limit may be just doing it’s job, what is the actual temp in the attic when the fan starts ?
Geo
 
  #6  
Old 07-14-19, 12:57 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 51,366
Upvotes Received: 206
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.
 
  #7  
Old 07-16-19, 03:02 PM
Member
Thread Starter
Join Date: Jul 2019
Location: United States
Posts: 3
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.
 
  #8  
Old 07-16-19, 03:35 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 51,366
Upvotes Received: 206
It would not be a flue related issue.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes