Gas furnace will not turn on when calling for heat


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Old 11-10-10, 07:54 AM
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Gas furnace will not turn on when calling for heat

When the cold weather started kicking in, I turned on the heat and set the temperature on the thermostat. The Heil gas forced air furnace did not start. So I turn off and on the power switch on the furnace a couple of times and then it starts up. It will work fine for awhile then sporatically it will not start up again. So I do the "off and on" switching again to start up the furnace. Is there a simple fix to this? Thanks.
 
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Old 11-10-10, 08:31 AM
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You need to take the cover off the burner compartment of the furnace. Get the model number off the rating plate in the burner compartment and post it here.

Also, carefully observe the sequence of operation of the furnace and post the series of things you see happening when the power is turned on to the furnace and the thermostat is turned up.
 
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Old 11-11-10, 08:03 AM
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The model number is NTG3100GFA4 or FBF100F14A4. When the power switch is in on position, I turn up the thermostat and this sequence occurs; 1) I hear the combustion blower and the exhaust fan (the fan in the can outside the house) goes on, 2) then I hear the flame ignitor sparking, 3) then I see a little pilot light goes on, 3) then all of the main burners ignite with blue flames with a wire in the middle turning orange, 4) moments later the circulating blower turns on, 5) then when thermostat reached called temperature, the flames shut down with the combustion blower shutting down too, 6) I still hear the exhaust fan still on and the circulating blower still on, 7) moments later the exhaust fan turns off, 8) moments later the circulating blower turns off.
Maybe after an hour or so, the funace does not turn on when the thermostat is calling for heat, so I flick the switch off and on to start it up again.
 
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Old 11-11-10, 09:01 AM
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That's an excellent description of the initial call for heat, which seems to be normal. But what happens during the subsequent call for heat when it fails to ignite?

It should light up reliably each time the thermostat is turned up. You should be able to turn the thermostat up repeatedly to get the ignition sequence started and to observe how far it gets before it quits.

What you are describing sounds like unreliable ignition ----sometimes it works OK and other times it doesn't. Usually that goes to a furnace that wont light up at all before long as the problem gets worse.
 
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Old 11-11-10, 08:51 PM
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I'll keep raising the thermostat and observe some more, thank you.
 
 

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