Heating intermittent on/off issue

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Jack1

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Came home last night, turned thermostat up, heard gas come on, than no fan, turned off, waited a few min. turned on, heard gas, and then fan came on a min. later. During the middle of the night heard gas come on, than no fan,
waited till morning. tried turning off again, wait a few min. turned on, heard gas, and then fan came on a min. later.
With nights at 25-35, it is cool to say the least if furnace does not work.

Side note may or may not be related. notice on stat. fan icon seems to be showing (Robertshaw stat. if I recall)

Any thoughts are appreciated.
Thanks!
 

Reach4

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30 year old natural gas furnace and the fan you are talking about is the blower fan?
 

Jadnashua

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Turn the power off to the furnace, open the access panels up, carefully (you don't want to bend the fan blades or squirrel cage!), and see if it rotates freely without noise. SOme older ones also used a fan belt, the belt could be broken, loose, or just plain worn out. Often, they use a relay to turn the fan on, it could be shot. There's usually a thermal switch that waits until the heat exchanger is warm before turning the fan on, it could be shot. IOW, there are lots of things that could prevent it from turning on. If the burner comes on and the fan won't run, there is likely an over-temperature sensor that shuts things back down to keep you from burning a hole in the heat exchanger or the house down. If you're not comfortable with this, find someone that is.
 

DonL

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Came home last night, turned thermostat up, heard gas come on, than no fan, turned off, waited a few min. turned on, heard gas, and then fan came on a min. later. During the middle of the night heard gas come on, than no fan,
waited till morning. tried turning off again, wait a few min. turned on, heard gas, and then fan came on a min. later.
With nights at 25-35, it is cool to say the least if furnace does not work.

Side note may or may not be related. notice on stat. fan icon seems to be showing (Robertshaw stat. if I recall)

Any thoughts are appreciated.
Thanks!

When it gets in hose mode, Does the Fan run if you go to Fan only mode ?

What brand / model are you working with ?

Jim's ideas should clue you into the problem. It is good to understand how your furnace works, If you plan working on it.

Do you have the Service Manual ?

Good Luck, Don't Blow Yourself UP. :eek:
 
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