I'd appreciate any advice on troubleshooting this issue. I have an old natural gas furnace made by Central Environmental Systems in York, PA. Model# P3UGD08N08001A, Serial# ENSM374304. I've been operating this unit since I purchased my home about 3 years ago. Each winter when I go to fire the heat up, the pilot light will not stay lit. I've gotten pretty efficient at changing the thermocouple after watching the service tech the first time. Anyway, this fall has been the same story, with a little twist. I installed the new thermocouple and fired the furnace up for a few days of cool weather. Weather got warmer, and I shut it down again for 2 or 3 weeks. Getting cooler again, and as I expected, the pilot light won't stay lit - with a basically new tc. I replaced it with another (2nd of the season), but my elementary troubleshooting skills have now failed me. I know I need a new, more efficient unit, but that's not really in the budget right now.
If it's not the thermocouple, what are the next steps? Air filter is good, breaker is good, power is good. I've got a multimeter, and I'm not afraid to use it. I'm fairly mechanically inclined, but being a gas furnace makes me second guess trying to fix it myself. However, the anticipation of the service bill may outweigh that.
Any advice or tips will be greatly appreciated.