Manage My Life

Why does the thermal fuse keep blowing in my dryer?

by Manage My Life Last activity date:
March 2nd, 2009

I have a Whirlpool Roper dryer model RED4100SQ0. The serial number is MT3422615. I have replaced the thermal fuse twice and it runs one cycle and the thermal fuse is blown again and needs to be replaced. What could be causing this?

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Dryers , Whirlpool , Building Supplies
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Answers (1)
Lyle W
Clogged or restricted exhaust vent air flow is the most frequent cause of a thermal fuse blowing. Check the lint screen for lint or a build-up of debris that could be inhibiting air flow through the dryer. Wash the lint screen with water and a nylon brush and then thoroughly dry it and replace it in the lint screen housing. Check the flexible vent hose behind the dryer for kinks or clogs. Check the exhaust vent duct system to the outside of the home for restrictions. You may need to have a service clean the duct system.

If you did not find any obvious problems in the exhaust vent system to the outside of the home, then I recommend conducting the following test:

Before replacing the thermal fuse again, try these steps:

Unplug the dryer to disconnect electrical power.

Temporarily tape the two wires that go to the thermal fuse together to essentially "bypass" or "jump" the thermal fuse. Use electrical tape to properly insulate the connection and avoid contact of bare wire contacts with the dryer cabinet. NOTE: Do not leave the thermal fuse bypassed following this temporary diagnostic test. The thermal fuse is an essential safety component that must normally be in place to safely run the dryer.

Reassemble the dryer and plug it back in.

Fill the dryer with a medium load of wet laundry.

Clean the lint screen and make sure it is properly in place in the lint screen housing.

Pull the flexible exhaust vent hose off of the back of the dryer so that it will vent directly into the laundry room.

Position the dryer so that you can measure the temperature of the exhaust air from the middle of the vent in the back of the dryer with an accurate thermometer.

Start the dryer on a timed cycle with high heat.

Measure the temperature of the air coming out of the middle of the exhaust vent behind the dryer.

The dryer should heat up to about 150 degrees. The heating element should then shut off until the temperature decreases 15 to 20 degrees. The element should then cycle back on. The dryer should continue to cycle between about 130 to 150 degrees.

If the dryer heats up way past 150 degrees, then you will likely need to replace the operating thermostat that is right beside the thermal fuse. You could also have a heating element that is shorted to the cabinet and heating constantly.

NOTE: Stop the dryer if it heats past 180 degrees. Do not let it continue to run and heat past this temperature.

If the dryer is cycling properly with the vent hose disconnected, then the likely cause of your thermal fuse blowing is the vent duct system to the outside of the home.

NOTE: Be sure to replace the thermal fuse before running the dryer beyond this temporary component test.

NOTE: If you are not completely confident in your technical ability to safely conduct this test, then I recommend calling a service technician to diagnose and repair the dryer.

If you need more help, resubmit your question with additional details.
by Lyle W
March 2nd, 2009
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