MT GAS DRYERS
That doesn't look like a HOH dryer to me the door is too large. In any case I believe a dryer this basic only has one operating thermostat. Yes it could be a bad timer but I would be sure that its really consistent about heating fine on premapress. Try drying a large load of towels on PP and see if it works. If it starts to not heat it could be bad gas valve coils, if it is the timer its very easy to test with a volt meter or ohm meter and you should be able to clean and or adjust the heat contact in the timer.