Any HVAC guys near Madison, WI???

[Jason Hanko]

Im having a little trouble with the furnace in my shop. Its a LP wall furnace that I picked up last year. It worked fine for a few months, but day the pilot light went out and I couldnt get it to stay lit. I tried a few things but Im no expert so I had a local company send a guy out - he told me it needed a new gas valve.
So I got a new valve and got it installed today - now the pilot light stays on just fine, but the unit will only run for about 5 minutes and then it all shuts off.
I can get the pilot light started right up again, but again after a few minutes of running the main burner and pilot will go out.
Ive monitored the thermalcoupler with my multimeter and I dont think thats the issue.
Anyone have any ideas or advice? What Id REALLY be greatful for is a shop visit from someone who actually knows what theyre doing. Ill provide the beer!!!

[Bruce Wrenn]

Does the furnace have a fan? If so, is it coming on. If not, then the high limit switch is shutting off the gas.

[Jason Hanko]

Hi Bruce,
Yes - the unit does have a fan. I think its supposed to be a dual speed fan - although it never kicks up into the higher speed. It has in the past, but hasnt for a while.
I just assumed that the gas was shutting off before it got warm enough to turn up to the higher speed. Could it be that the fan is trying to jump up to the high speed but is unable to, and thats triggering some sort of safety shut off?

[Bruce Wrenn]

Jason, it still sounds like high limit switch is cutting off gas. High limit switchs can either be a "snap switch, or a single use switch." If you have a filter in air return, is it one of those pleated high eff. ones? If so, it could be restricting air flow enough to trigger high limit switch. Put in a new filter, or one of those cheap ($1) fiberglass filters. If you have duct work, are vents open all the way? Turn fan to the on position and check each outlet for air flow. Do you happen to have, or can you down load owners manual. Often there is a "trouble shooting section." Check actual fan for a nest from an uninvited guest. I can tell you a mouse doesn't last long going around in a fan.

[Jason Hanko]

Thanks for the help Bruce.
The unit doesnt have a filter (not yet anyways, I was going to add that once I got it working). I can see the fan and theres nothing in there. There is no duct work - Its one of these.
It does sound like some sort of limit switch issue like you are describing - it will be going along fine and all of a sudden theres a click and both the pilot and main burner will immediately shut off. The pilot lights right back up again when I go through the pilot-lighting process, and will stay on indefinitely if I dont try and actually run the unit.
Ive played with it a little and read through the manual a few times - from the troubleshooting section it seems like either the fan is re-circulating the warmed air (although I dont think this is too likley) or there is some issue with the venting that is tripping the safety (not sure how to check this tho). As best I can tell my vent pipe isnt leaking...maybe Ill take my CO detector out there this weekend and put it near the unit with it running...
Thanks again for any additional insight you (or others!) might have!

[Leigh Betsch]

I had a similar problem last winter in my shop. The the little fan/blower unit was bad, not the big circulating fan but rather the small unit that blows air thru the heating chamber (I think).
Then later in the season I had my vent pipe plug with ice. In both cases the furnace would shut off soon after it lit.