G.E. Gas Furnace problem


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Old 12-27-09, 11:00 AM
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G.E. Gas Furnace problem

I have a General Electric Gas Fired Warm Air Furnace; Model # 21LH100E2B3. It was made about 1978. It was working up until 2 days ago. Here's the problem: When you turn the thermostat on, you can usually hear the furnace lighting in the attic after a couple of seconds. It's not doing that anymore. When I went into the attic to check on it, the thermocouple is lit, shooting its flame, but the furnace will not light. If I turn the pilot off and start over, as soon as I light it, it goes right back to the thermocouple shooting its flame, but the thermostat is in the off position. I'm not sure, but I seem to recall that when you first light the pilot, it is a small flame, and the thermocouple will will not shoot out until the thermostat is "on". I don't know if there is a thermocouple problem or maybe a thermostat problem. The latter is only about 4 years old. Any help is appreciated. Thanks
 
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Old 12-27-09, 11:56 AM
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Leave the thermostat turned down.

Light the pilot so that it will stay lit on it's own.

Turn the gas valve control to the on position.

Then turn the thermostat up and the furnace should light normally.

The gas valve must be in the on position in order for gas to flow to the main burners.
 
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Old 12-27-09, 03:06 PM
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It sounds like he has one of those 2-stage type pilots where the pilot increases in size with the call for heat, just as some gas ovens do. And tiger is right in the sense that this type only gains in size when you turn it on.
 
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Old 12-27-09, 03:46 PM
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I've never seen that kind of ignition system on a furnace, Ecman, although mercury bulb type systems were used to verify that the pilot was lit before turning on the main burner gas.

I don't recall ever seeing a system that had that kind of high and low pilot outside of a range oven.

Perhaps we'll find out what Tiger has for an ignition system if he returns.

It sounded to me like he was hesitant to turn the gas valve to the on position.
 
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Old 12-27-09, 08:21 PM
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Hmm, might be a weak tcouple that drops out the safety, coupled with a bypassing gas valve. That would account for the small pilot flame. When you depress the reset button, this allows more gas to pass enlarging the pilot flame and heating the tcouple. I've encountered this in a few instances. Not sure if this describes what you are noticing or not.
 
 

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