Gas furnace runs for 15 - 30 minutes at a time

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Old 01-20-11, 08:01 PM
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Gas furnace runs for 15 - 30 minutes at a time

I set back temp to 60 at night. When my Carrier gas furnace kicks on (set to 68) in the morning it will run for 20 to 30 minutes. Then the burner shuts off and the fan blower runs till cool down. Two minutes later the furnace fires up and runs for another 20 - 30 minutes. This continues till it reaches the 68 temp setting. All of the vents are open and the filter is clean. Someone told me that it sounded like the flame sensor but from what I have researched, I don't think so. Got any ideas?
 
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Old 01-21-11, 01:49 AM
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You need an AC multimeter to check and see what is turning the furnace off. The most likely things shutting the furnace off would be the thermostat, limit switch or pressure switch.
 
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Old 01-21-11, 04:42 PM
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I would jump out the thermostat first by twisting the red (24 v) and the wire hooked to the w terminal (usually white) togther and see if it stays on. If it doesn't then proceed to the furnace to check limit (controls burners) or pressure switch to see if you have 24 volts present.
 
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Old 01-30-11, 06:42 PM
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Thanks guys - Interesting that earlier this week the furnace stopped functioning. I called Top Notch furnace repair and while he was checking the system I told him about the problem that was occuring. He checked the pressure switch and it worked fine but he was getting inconsistant vacuum readings from the pressure port. Turns out that the gasket on the exhaust motor was bad so the amount of vacuum pressure dropped below the required amount, shutting the system down. He sealed the gasket and the furnace fired right up. We both thought that the problem was resolved. Nope - the next morning the furnace shut down in 20 minutes for 60 seconds. Then came back on for another 20 minutes. I know that I should have had him check the limit switch and the thermostat before he left but we both were fooled by the vacuum leak. The problem does not seem to be getting worse so I can't justify the $'s for another service call. It's frustrating but I can live with it for now.
 
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Old 01-30-11, 07:41 PM
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ensure no air flow restrictions. ie filter or plugged evap coil. also furnace may be overfired, you would need a manometer to check gas manifold pressure. This check really needs to be done by a PRO
 
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Old 01-31-11, 05:16 AM
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Also, make sure you don't have any vents closed or blocked off.

I'd call them back saying the problem was not fixed.
 
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