[PizzaBob]

Hello, all, new here...

OK, I have a Rheem gas furnace in the crawlspace which is original to the house (1984). This place was vacant almost two years before we moved in three years ago. Before the first winter I tried to fire up the heating system and could not light the pilot. A little troubleshooting revealed a piece of grit in the pilot orifice, which, when excised, solved the problem. I also used compressed air to blow a lot of rusty debris out of the burner rows as well. Everything has been great until this last week.

The pilot light has been going out regularly -- at first once a day or so, then after each heating cycle. The thing stayed on all summer last year and now goes out a dozen times a day.

At first I considered a defective thermocouple but realized that wasn't likely since once lit, it stays lit and the T/C detects that it is heated after only 5 seconds or so. That's all the longer I got to hold the button down.

So I decided to watch the burner in action. After being on for a few minutes I noticed that the pilot went out while the rest of the burner was going full blast. There were also times when part of the burner seemed to not be burning and then the flames would slowly migrate back over the "dead" area. Ain't never seen nothing like this before. When the burner shut off, with no pilot that's all she wrote.

Thus I experimented some more and discovered that if I back off the gas valve control about 25 percent from full "on" toward the "pilot" setting, the reduced flames were much more "stable" and the pilot is no longer going out. Weird.

The valve has always been full on since we bought the joint. My suspicion is that gook has partially clogged the gas valve. Does it have a cleanable screen somewhere, perhaps, or do I need to hit Ebay for a replacement? Or am I on the wrong track, altogether?

Thanks kindly for any help!

[NorthernHeat]

It is snuffing it self out because it is not venting/drafting very well. Probable cause is a plugged heat exchanger, maybe the chimney, less likely because it will splill out the draft deverter, probably tripping the spill switch. I would also check it well for cracks or rust holes in the heat exchanger.