Well, at the risk of stepping on someone's advice toes, I would suggest a different first step. The thermocouple is the little thing the flame goes around when it turns up a little. The oil in the bellows (the little tip inside the flame) expands and opens the safety valve. If the flame rises but does not open the safety valve (flame from main burner), the thermocouple is likely the faulty (and less expensive) part. The thermostat's job is to raise the flame size and sense the oven temp and shut off gas when temp is reached. Just my $.02 from 35 years on appliances. Hth
