Do you have a voltmeter? If so, you can use it to determine if voltage is getting to both coils or not. Just be careful, the coils probably operates on 240 Volts, the rotational motor probably runs on 120V. You don't say if the temperature on high heat seems cooler than usual, but I would expeect that if the thermostat went bad, you would get too much or not any heat. You can always clip lead around the thermostat and see if the heat then gets as hot as it used to.