What Causes the Thermal Cutoff to Keep Going Bad on a Dryer?

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A thermal cutoff or switch is a safety feature found on many dryers. It prevents the dryer from overheating by cutting power to the heater if the temperature inside the drum reaches the cutoff’s preset activation temperature. Once it triggers, the component is bad; replacing it is the only way to return your dryer’s normal heating function. But you should only replace a bad cutoff after you’ve figured out why your dryer is overheating; otherwise each new cutoff you install will likely trigger and go bad quickly, too.

Lint Buildup

  • Lint that falls off fabrics can accumulate in your dryer’s vent and constrain airflow. If airflow becomes restricted, the drum’s temperature can’t be properly regulated, and overheating is possible. Of course, if the temperature elevates to an unsafe level, the thermal cutoff will immediately turn off the heater to allow time for the dryer to cool. Ensure that the dryer’s vent is completely clear of debris, and clean it if blocked. The dryer’s manual should list a set of vent cleaning instructions for you to follow.

Cycling Thermostat

  • A cycling thermostat monitors the dryer’s heat settings and, after a certain temperature is achieved, directs the heater to stop producing heat. If a cycling thermostat breaks, the heater may never cycle off, causing the air temperature to rise rapidly until the thermal cutoff activates to stop it. Because each cycling thermostat corresponds to a heating setting -- low, medium or high -- on your dryer, you may be able to determine which thermostat is bad based on the heat setting that causes the cutoff to go bad. Once you identify the faulty thermostat, replace it.

Safety Thermostat

  • A dryer that has a thermal cutoff also has a safety thermostat. The safety thermostat is often near the vent exhaust and connects to the thermal cutoff. The safety thermostat is preset to a temperature that overheating is imminent. If the thermostat’s trip temperature is wrong, however, or the thermostat isn’t able to record the air temperature properly, the faulty thermostat can cause the cutoff to trip prematurely. Contact a dryer repair technician to evaluate the safety thermostat’s performance. Change it out if the technician determines the safety thermostat is defective.

Heater

  • It’s possible that your dryer’s heater is generating too much heat and isn’t aligned with the heat setting temperatures programmed on your dryer. Contact a dryer repair technician to measure the heater’s output. Have him adjust the heater if needed. In certain cases, you might need to replace the heater to correct the overheating problem.

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