How Dryer Thermostats Work

Typical Dryer Thermostat

Dryer thermostats use a bimetal to switch the heater on an off. A bimetal is two small pieces of dissimilar metal bonded together that will “flex” or bend at a very narrow temperature range. When the bimetal (bi-metal) flexes it opens a set of contacts interrupting current flow to the heater and turning off the heat. Since dryer thermostats are always located in the airflow after the heater turns off the air cools and the bi-metal flexes back to switch the dryer heater back on. When the vent is restricted there is no air movement across the thermostat and it does not open its contacts to turn the heater off. That’s where the high-limit thermostat and or the safety thermostats come in to operation.

Notice in the drawing that the thermostat #15 is located in the airflow on the backside of the blower housing.

Bimetal thermostats are used in devices through your home. The thermostat in your coffee maker is most likely a bimetal thermostat. Because bimetal devices warp at specific temperatures the mechanism that allows your toast to pop up is probably one.