We been having problems with our 20 yrs old Carrier furnace (model# 58GSC065). The furnace has a electric ignition system. After the pilot flame turns on, sometime the heat exchanger burner won't go on, sometime after the heat exchanger burner flames on the blower won't turn on. We suspect it maybe a defective thermocouple issue (not sensing the flame???) but need some expert opinions. Any help will be greatly appreciated. Thanks. PS We did take out the pilot assyembly and try to clean the thermocouple once before. It got a bit better but then went back to the same problems I described above.