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I have had a reoccurring problem with my Rheem gas hot air furnace. Model# RGVC 07EA ER and
SER #KN5D1041F47889671. This is a 28 year old furnace that is a horizontal attic mounted furnace. I have had many service calls, with professional techs, costing hundreds of dollars with parts and labor to no solution. It is rather a long description but I would like to give you all the know symptoms and all the parts that have been replaced thus far so you have as much info as I can give you. If you need pictures of the control area I can get some and email them to you. No one and I mean no one has conquered this problem as of yet. I even tried justanswers.com to no avail.

SYMPTOMS:

This unit functions as should when the temps are near or above freezing. The unit produces great heat and runs well with no unusual noises or sounds or smells. This furnace will run all day and into the night. It usually starts to act up around the later evening or very early morning hours before sun rise. The temperature is at its lowest and the attic is freezing cold when this occurs. When the thermostat calls for heat the inducer fan comes on, the pilot lights up and tries to light the main burner but that fails to ignite. It usually does this a few times before locking out.

The problem will sometimes happen in the daytime hours if the sun is not out (or heavy overcast conditions) and the outside temp is below freezing. This occurred on 4/1/17 when a quick cold snow blowing noreaster blew through. I can get it up and running, most times, by shutting off the emergency shut off switch. I let it sit for 45 minutes or longer with the thermostat in the off position and the temperature to the lowest setting on the thermostat fan on "auto". I turn the main power back on, turn the thermostat back on and set the temp to a high temp setting like 78 degrees F because the house is now showing a temperature of 64 degrees F. I put the blower fan in the "on" position and the unit works ok, runs as it should but only with the blower fan in the "on" position. Once the sun comes up and the temp rises to over freezing the thermostat unit can be placed back in "auto fan" position and it works with out fail. Usually it quits in the wee morning hours while we are asleep so we wake to the cold drop in temperature.

This unit had no control board but has a S86F Honeywell Intermittent Pilot Non 100% Shutoff Natural Gas Only controller. Case in point as of 4/3/2017: 3am temp was around 25 degrees F. Furnace quit. House temp dropped. Did the reset and following procedures at about 4am. Got up at 6:30am restarted the furnace with the blower fan in the "on" position. Unit fired up and began to heat the house. By 9am I placed the fan in the "auto" position on the thermostat unit is up and running perfectly. The outside temperature was now 47 degrees F. The outside temperature at 6am was 29 degrees F, at 7am 30 degrees F and at 8am it was 38 degrees F.

PARTS REPLACED TO DATE:

Inducer Fan, F&L sensor, air switch and blower fan center relay and a used S86F that was from a known working Rheem gas furnace. (I still have the original but no way to test it out.)

My Rheem furnace parts diagram can be viewed here.

Every service tech thinks I am nuts and this can not happen as described. May I pick your brain for a solution? Any help would be above greatly appreciated.

  • Have you tried replacing the thermostat? – Mysterfxit Apr 5 '17 at 11:50
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    So the unit is in an unconditioned attic? What is the ambient temperature around the unit when it fails? Is there a drip leg in the gas line? When the main burner fails to ignite, can you hear gas flowing from the burners? – Tester101 Apr 5 '17 at 12:06
  • Almost surely is the thermostat. Replace it and it'll be fine – DDS Mar 26 '18 at 10:33
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You could be losing gas pressure

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We had a problem almost exactly like this with our first high efficiency furnace, had to get the tech there at 5:30 am so he could witness it first hand. Turned out to be the air intake pipe - they used too small a diameter for the temperatures we were getting. Once bigger diameter piping was installed, the furnace worked fine.

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