Hi:
I have a Heil Model 1002612-A Furnace (about 14 years old) that's driving me nuts!
The furnace cycles are inconsisent. Furnace comes on, pilot lights but burner doesn't always ignite. Runs for 6-7 minute cycle, then shuts off. When it gets cooler, furnace will go through a complete cycle motor on, pilot then burner ignite. Cycle runs 6-7 minutes.
Service tech, cleaned valve but did not help. He suggested that the thermostat may be the cause. Replaced thermostat. Suggested that it may be the "spark box". That part was replaced. This morning I observed furnace operation. Furnace would run for 6-7 minute cycle and burner would not ignite. 5-6 minutes later, full operation cycle for another 6-7 minutes. This went on for 2 hours until I turned thermostat off.
Leaving the thermostate off and letting the house temperature cool, I turned themostat on and complete cycle (pilot-burner-blower) would occur. Its when I leave it on for the day that the inconsisteny occurs.
Any suggestions (inlcuding taking an axe to it!) would be appreciated!

Try to find the real model number. The number you listed is not a Heil furnace number. It will be located on a tag with a bunch of other info inside the burner service door area usually on the side or front wall. I need to find out what company made the gas valve/spark box OR can you post the model number of the spark box and gas valve along with the manufactures name.

Thanks so much for your response. My knowledge of furnace operations is extremely limited.

The Furnace Model No (inside service door) is :
NUGE 075BG01
867 768142
Serial No. L913564093

The new sparkbox is mfgd. By Honeywell and has the numbers
"S8610U" (24-v)

The relay switch is a Tridelta Industries Model FS6441-719

Here is your install manual for the new control you have.


http://customer.honeywell.com/techlit/pdf/69-0000s/69-1955.pdf

It is possible the new control you have is intermittent or

If a new cable to the ignitor was not installed when the spark box was replaced it could be the cable you can try and cut off a 1/4 inch or so on each end and reassemble just in case it is getting a bad connection.

Thanks much for your efforts. We'll give it a try!