Heil furnace burner turns off

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Old 01-31-17, 06:36 PM
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Heil furnace burner turns off

HEIL gas furnace 27 years old located in hall closet, LUX digital thermostat on wall opposite furnace, old Honeywell dial type limit switch unit. Outside temps 50s during day 30s at night.

Furnace works fine all day and evening. Only fails early morning 2-5 am. We wake up to a clicking ignitor, pilot light, vent blower and main blower running. No gas to burners. Thermostat still shows demand for heat meaning flame indicator flashing. Burner is shutting off at 170 deg, no where near the 210 deg limit switch setting as read on the limit switch dial. Have found if the furnace closet door is cracked open when going to bed the furnace runs fine through the night. I have run it without filter, changed filter and cleaned combo ignitor/flame sensor. To me everything points to overheating except the point it fails is not near the high limit. Any suggestions?
 
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Old 01-31-17, 07:44 PM
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Burner is shutting off at 170 deg, no where near the 210 deg limit switch setting as read on the limit switch dial.
The heat exchanger better never hit 210 or you'll have rubble on your hands.
Even 170 degrees is too high.

You need to check airflow thru the furnace.
Sounds like a return air issue if it runs fine with the door open.

You should check heat rise thru the furnace. You check the return air temperature right before the furnace and the supply air temperature right after the furnace. Subtract them and you'll have the heat rise figure.

It will usually be 30-35 degrees.
It will be posted on the ID tag on the sidewall inside near the burner.
 
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Old 02-02-17, 05:43 PM
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Checked two neighbors identical furnaces both high limits set at 210. One read 160ish deg. when on and the other 170ish. No more than the typical problems over the years. Should we be suing the contractor?

"Check...supply air temperature right after the furnace". Can that be at the closest room vent? If so I'm seeing 68/69 deg at the return inlet (right below furnace) and 138 deg at the first vent, about 15 feet from the furnace and read about 10 minutes after blower comes on. Temp rise on sticker says 35-65.

Furnace runs fine through the night with the closet door cracked open. There's two air source openings in the furnace closet. One a 6 inch open duct coming down from the attic on the ceiling and one a 14X6 inch hole cut in the wallboard between studs near the bottom right side. It appears these are the air sources with the closet door closed. Both are clear. Still scratching head about why it only fails early morning.
 
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Old 02-03-17, 01:26 PM
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If you use night setback then the furnace may run for a long time in the morning to recover.

You would want the rise to be close to average than pegged at the top. Your rise is 70.

I am not an authority on furnace installations as I strictly service them.
A heat rise of 70 is too high.
I feel a plenum temp of 170 is too high.

Can you post the model number for your furnace.
It will be on an ID tag on the inside wall near the burner.
 
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Old 02-03-17, 07:43 PM
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Don't use the setback function. Wall tstat is set at 71 deg day and night.

Heil NUGE075CH02
 
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Old 02-13-17, 03:22 PM
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Decided to replace the furnace and A/C. System was 27 years old and didn't want to throw money at it. On removing the evaporator found it 80-90% clogged so figure that was causing a lack of airflow and intern, the burner cutoffs and banging or oil canning as the HVAC techs called it. Thanks for the inputs.

BTW - With the new furnace (Lennox signature elite with 2 stage burner and multi speed blower) the temp at the first vent maxed at 105 deg. Was hitting 145 deg with the old furnace. Sound better? I can't see the limit switches on the new furnace. I've let my neighbors know. Furnace now runs about 10-12 minutes at each cycle with much better airflow at each vent instead of around 30 minutes with the old furnace. Much quieter too. I'm happy.
 
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Old 02-13-17, 05:03 PM
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Since the evaporator was so clogged..... it sounds like maybe no air filter.
Be sure the new furnace has an air filter that can be replaced.

Thanks for letting us know the outcome.
 
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Old 02-15-17, 01:24 PM
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Ya, you would think so but no, I changed filters every 3-4 months. The last few weeks after the problems started I did run it with a new filter popped up some to keep it from short cycling so the air was only partially filtered. Another contributor may be the fact except for the kitchen the house is entirely carpeted with what I call short shag carpet. Lots of fibers. That and we've always had cats and dogs. Course the house was 15 years old when we bought it. Who knows what care was taken previously. The old furnace used a one inch filter. The new furnace uses a two inch filter so that may work out better. We'll know in 25 years - lol. Thanks again.
 
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