This commercial coin-operated unit is about 10 years old and works fine except for the following: The igniter comes on and about 5 seconds later the flame comes on. Unfortunately, the flame only stays on for about 10 seconds then goes off. About a minute later the cycle begins again and keeps repeating (on and off). As a result the tumbler area gets warm, but not hot, and the clothes take an inordinate amount of time to dry. I gave the motor/flame area a thorough cleaning and checked the vent for obstructions. Problem continues. Your thoughts?