I have a 1980 Payne Model 396GAW00075 furnace and it will start up, the fan comes on and run for about 3 min. then the burners will shuts off and about 30 sec. later it will turn back on. It will do this about 4 to 5 times then stay off until you shut the power off to the furnace and wait for about 30 min. and turn it back on. It will then repeat the same cycle. I have repaced the thermostate, cleaned the pilot and electronic ignition probs and checked all the electrical connections. I have cleaned the burners and furnace every year since 1994 so I am a little familiar with it, but it has me stumpped this time. Please help