I have a Bryant Plus 90 furnace that has operated well for years. Last Monday the outside temp dropped to 3 degrees... I woke due to shivering and realized that the furnace was not operating. I checked all the fuses and everything else I could think of and when I replace the skins the furnace turned on and seemed to run as usual. This only lasted a short time,and after trial and error I can get it too run for about 45 minutes at a time only after turning off the thermostat for about 30 minutes then turning the thermostat back on. The furnace starts normally but shuts off after 45 minutes or if it reaches the set temp. Even if it turns off at the set temp it will not restart. I called a number of furnace companies and they charge an average of 75 dollars just to show up then $300 to look at a furnace, this cost is not including any parts or labor. Since this cost is way beyond what someone of a disability pension can afford I have been heating my home 45 minutes at a time. I have checked the blower too see if the bearings are bad and it moves as freely as it always has. There are no noises or any other symptoms of failing parts... except that is that it shuts down for no good reason... can anyone help?