My Kenmore gas dryer was running for 10 hours on the auto cycle. When I restart it the burner would fire for about 10 minutes, shut off and then it would not fire again. The igniter glows but it won't fire. I open the door to stop it, start it back up and it repeats the above. I found a plant outside had fallen in front of the vent so after clearing that out I took the back off and cleaned the entire exhaust ductwork. I put it back together and got the same thing. I replaced the thermostat, internal bias (part# 3387134 41) thinking the heat burnt it out and thought it was fixed because the burner stayed on for 15 minutes or so but then the same thing happened. Any ideas?