...::: GE Gas dryer have to hold button in to run

It all started when I would come down to the dryer and found it had stopped, then it would run ok the next few times then I found the first time I used after in ran good a few times as soon as I released the start button it would stop running. I found if I held the button in till the burner started the dryer would run and complete the cycle drying the clothes. Now it only runs/dries when the button is held in or taped down. is this the centrifugal switches in the motor or is it the broken belt switch on the tensioner.