Gas furnance continually kicking in


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Old 01-04-08, 10:36 AM
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Gas furnance continually kicking in

I have a 1988 Carrier gas furnace with automatic ignition. I live in MN, 3 story split level. I have the thermostat set at 66 throughout the night and day and then increase the stat to 70 when home from work. Recently I noticed that when I increase the stat to 70 when I get home the furnance/burners will continually kick in, even before the blower has stopped running. Near the end of the blower cycle you can hear the ignition clicking in to reignite. This was not an issue in the past as I have had the stat at 72 in the past and do not recall having it continualy run. If I turn the stat back down to 66ish at least the furnance will stay off for 6-8 minutes before kicking in again. The stat is located on the main floor, on a wall abutting the garage. The upstairs is boiling while the main level and lower level are cold.

Any thoughts on why furnance continually cycles despite only being set 2 degrees higher than during most of the day and the fact that last year i didnt have this problem and had the stat set above 70?

Does this sound like a bad thermostat (it is the original honeywell turnstyle model)?

We had our furnace checked last year and it checked out fine and the burners are blowing a nice blue flame. Any info would be helpful.
 
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Old 01-04-08, 12:39 PM
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More than likely, it's the thermostat which is turning the furnace on.

What is the model of the thermostat?


Non digital thermostats often have a heat anticipator which, if improperly adjusted, will cause the furnace to short cycle the way you describe.

Take the cover off the thermostat, and look for the model number and describe what you see and observe as the furnace cycles on and off.

You may see a heat anticipator, which often has a dial reading from .25 to 2. or so. If so, what is the reading of that?
 
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Old 01-04-08, 02:07 PM
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I do not currently know the model number. However, i did check the anticipator number and believe it is around the .4 range right now.
 
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Old 01-04-08, 02:36 PM
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You need to observe the thermostat and see if it is responsible for cycling the furnace on and off.


The alternative is that it is staying on even when the furnace burners shout off.


What do you see happening?
 
 

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