Have the same problem with my 1975 Payne: When it starts out in the am, it will run for 30-40 seconds,the burner will stop, but he blower will continue for a short time. Within 15 seconds, it will re-ignite, the burner will stop, and the blower will continue for a short while. I had a service man check everything, including the thermostat. When he ignited the burner, by by-passing the thermostat, the same thing happened. He determined that the main board circuitry is worn and needs to be replaced.