I have a no thrills Estate gas dryer the flame will stay on for 30 seconds then drops off. I cleaned the whole entire dryer inside and out. Pulled off vent tube, same problem. The glow plug will just recycle turning on and off without turning on the flame. I replaced the coils, and that didn't help. Tested all the sensors for continuity, and they tested all good. This dryer doesn't have a circut board just a timer switch. Help!