Gas dryer only dries on timed high heat and only when setting timer to 60 minutes or more. The pilot lights and dryer will work fine. On automatic low heat or automatic high heat no drying at all. I did replace thermal switch in back bottom of dryer by vent. No change. All vents are clean. Would the coils be bad? Or is there another temp regulator for the different drying cycles? Any help would be appreciated. Thanks.