Heil furnace problem

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Old 11-04-11, 06:47 AM
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Heil furnace problem

I have an older heil furnace model NUGI075DF03 The pilot light lights for about 3 seconds then shuts off the main burners dont light. This process will keep repeating itself. Question is how do I determine if it is the ignition sensor, pilot module or the gas valve. Any help would be appreciated.
 
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Old 11-04-11, 09:33 AM
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I presume you have a Honeywell intermittent pilot ignition system, usually a Honeywell 86XX model ignition control?

Observe the sequence of ignition carefully.

The gas for the pilot burner and spark should turn on together. The spark should remain on until the pilot burner lights, then shut off immediately.

The gas for the main burner should turn on and light within a second or two off the pilot burner.

The main burners should remain lit unless the pilot burner shuts off or the thermostat shuts off the furnace.


That's the way most of these furnaces work. There could be a flame sensor on the side opposite the pilot burner that checks to see if the main burners have lit and would modify this sequence. If there, it would be a rod sticking up into the burner flames with a wire coming out the bottom and going to the ignition control. Let me know if that is there or not.
 
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Old 11-04-11, 10:04 AM
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You are correct it is a honeywell the spark stays on and the pilot comes on the spark shuts off. the main burners never come on and the pilot shuts off after 3 seconds or so. then the whole process starts over again. A few years ago I was told to clean the flame sensor with steel wool I did then and it worked ok. used fine sand paper. No such luck this time. Can I use fine grit sand paper on it or is that going to ruin it. Thanks for your help
 
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Old 11-04-11, 11:46 AM
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Sorry but to answer your question there is only 1 flame sensor and it is part of an assembly with the pilot light attached to it
 
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Old 11-04-11, 12:36 PM
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Since the spark shuts off, the ignition control is detecting that the pilot light is lit. The next step ought to be that the main burner is turned on.

The pilot light should remain on as long as the thermostat is calling for heat, even if the main burners don't light.

Since the ignition control isn't doing what it should, you have a bad ignition control that needs to be replaced.

Still, I'd check to see if the main burner gas is being switched on by the ignition control. Check to see if you have 24 VAC on the MV wire at the gas valve. Probably not, but perhaps worth checking.

I suppose the gas valve is turned to the on position?
 
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Old 11-04-11, 01:05 PM
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I will check that tonight when I get home. I am in electronics and have access to external power supplys. Do you think if I inject 24v on the mv wire when the pilot comes on that the main burners should light or not. Just a thought. Thanks so much for your help
 
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Old 11-04-11, 03:52 PM
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24VAC. Yes, but that's not necesary to test what's happening, and if you do things wrong you could wind up with a face full of flames.

You can disconnect the wires to the gas valve and check for continuity across the gas valve solenoid.

But if the ignition control isn't providing that 24VAC when it should, you have a bad ignition control module.
 
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Old 11-05-11, 08:12 AM
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Yes when I checked the pv wire I see 30vac then the relay kicks in the mv wire only gets to 10vac which isnt high enough to trip the relay I also disconnected the gas and put 24vac on the mv wire and can hear the relay trip so, I have to assume at least the gas relay is ok. Is there any way to check if the sensor is doing its job everything happens so fast I am not sure the sparking is stopping or not. The pilot light comes on but the sparking doesnt stop until right before the whole process is about start all over. Please let me know thanks again
 
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Old 11-05-11, 08:51 AM
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The metal cage surrounding the pilot burner serves as the flame sensor. Yous can brush off that metal with a wire brush which would clean off any oxides preventing the pilot burner flame from being detected.

I really never encountered problems with the flame sensor being dirty with this style of ignition system, although I've heard this reported by some others.

You have a bad ignition control that's failing to turn on the main burner.

I'd replace it.
 
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Old 11-05-11, 10:55 AM
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Thats what I will try thanks so much for your help
 
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