I have replaced virtually all thermostats and thermal couplings and cut offs - and have checked continuity on the heating element - it is good. The heat was working until yesterday but we had suspected for the last couple months that it was not working all the time. yesterday it stopped working for about two hours of running then came on for about 1 hour - now it has not come back on in a few hours running. The vent tube appears clear - I feel strong airflow when running the dryer without heat. I have shut the circuit breakers on and off - they did not seem tripped. Any ideas out there why it is not heating?