If you suspect you have a faulty dryer thermostat, you should first check the dryer ventilation restriction. Since the dryer control thermostats are in the air flow leaving the dryer, a dryer thermostat cannot operate the dryer heater if there is no air passing through it. If you have a ventilation restriction, your dryer will get too hot. You may notice that the tumble dryer is hot on top, there is very little lint in the lint filter, and the laundry takes a long time to dry. This is the reason why most people want to check a drying thermostat.
If you are sure you do not have a dryer ventilation restriction and want to check your dryer's control thermostat, you must first disconnect the dryer from the electrical supply and access the thermostat. Thermostats are located in different locations on different brand name dryers. However, a control thermostat will always be in the air stream. In other words, the side of the thermostat that senses the temperature will be exposed to the air flow from the dryer. Do not confuse control thermostats with high limit thermostats or dryer safety thermostats. This type of thermostat detects direct heat from the heater.
Okay, now that you have gained access to your dryer's control thermostat, checking a thermostat is simple because it has an electrical input and output path. Use an ohmmeter and check continuity, there should be no resistance. Technicians check to see if a dryer thermostat is cycling using a voltmeter. When a dryer is running and the thermostat cycles, the voltage across the thermostat is 220 volts. A non-technical technician should never check the dryer thermostat while the dryer is plugged in. An inexperienced person should always make sure that the dryer is disconnected from the power supply and use an ohmmeter to check continuity.
It is not necessary to remove the thermostat from the dryer to verify this. However, it is very important that you remove at least one of the thermostat wires so that the only electrical path you will read is on one side of the thermostat and off the other. As you will check the thermostat at room temperature, the electrical contacts inside the thermostat will close. In other words, the circuit will be completed on one side and on the other. The resistance reading on your ohmmeter will be zero, indicating that the electrical path through the thermostat is complete. If the electrical path is completed through the dryer thermostat and the dryer does not heat up, the problem is not the dryer thermostat. This article is also good for washing machine repair information.