I have a 1989 Coleman direct vent (sealed combustion system) forced air furnace equipped with standing pilot
Model 7665-856
Serial 048272343

This problem only occurs when it is really cold outside. When I need the furnace the most. The furnace starts up normally. Burner turns on then fan turns on. Burner turns off and on as needed. Then both turn off at same time. I'm guessing it's the high temp switch that pops out but is not pushable yet. Furnace cools off for about 20-30 minutes and blower turns on for about 15 seconds then turns off. Button is pushable and cycle starts over except this time burner only goes on about once or twice before they both shut off. What do I need to do/replace? Any help would be greatly appreciated. Also where is the best place to get the parts. Thanks a lot:D

It sounds like the high limit switch is bad. I would remove it and take it to a HVAC or electrical supply, and let them match it.