Dryers nowadays typically have two thermal fuses, an operating thermostat or thermistor, and an element or burner overheat thermostat.

The operating thermostat / thermistor is on the blower or exhaust air housing and controls the target temperature of the drum (high, med, low, whatever is selected for the cycle).

The overheat thermostat is on the element or burner housing and cycles the heat source if airflow is impaired, which causes the heat source to get too hot. It automatically resets when the element or burner cools (the dryer does not turn off) and the heating resumes.

One thermal fuse is on the blower housing. It triggers if the operating thermostat fails and the drum temperature gets too high, shutting the entire machine down before the clothes could catch fire.

The other thermal fuse is on the element or burner housing and serves as a failsafe for the overheat thermostat. Also as a failsafe in case of an electric element shorting to ground (such as if the element breaks and touches and heater box, in which case the overheat thermostat won't kill the power to it if it overheats).

Ive watched several troubleshooting videos for this specific model troubleshooting for no heat. Each video tested the High-Limit Thermostat, Operating Thermostat, Thermal Fuse, heating element. One of the videos tested the timer. None tested or even mentioned the Thermal Cut-Off Fuse.

The thermal fuse on the heater box typically doesn't shut down the entire machine on a WP-built unit, just prevents it from heating ... leastwise not on older models, a new one on the sales floor today may vary. Other brands also may vary in that behavior. The thermal cut-off on the exhaust duct (as a fail-safe for the operating thermostat/thermistor) usually does make the dryer dead.

In either case of a blown thermal fuse device, the paired thermostat or thermistor should also be replaced being that the thermal fuse is a fail-safe for it. Unless of a case that an electric element is shorted to ground, in which case the high-limit thermostat may be OK but it's still recommended to replace both.

Before I purchase new cut off, I decided to test the two thermostats:

one is marked L155-25F. it opens at 110°F.

the other L250-80F. it opens at 180°F.

Some sites say that number after the dash is +/- for opening temperature. Other sites say that is how much less the temp needs to be for closing. I dont know which sites are correct.

The L number is the limit temperature. The -number is the differential.

*L155 (operating 'stat) should turn the heat off at 155°F and back on at 130°F.

L250 (high-limit) turns the heat off at 250°F, back on at 170°F.

How are you testing?

*If your L155 has four terminals, one pair is for a bias heater that generates a bit of internal heat to make it trigger at a lower air temperature. It energizes at heat setting less than High (Low, Med, etc.). This is a way to design the machine with only one operating thermostat instead of separate thermostats for each temperature setting.

A down pillow blew up inside my dryer resulting in tripping the thermal cut-off fuse/ switch. The dryer operated but did not heat.

After diagnosing the probable cause, I removed it and was going to order a new one. I had my son test it to confirm the results I had when I tested it. I had read somewhere that you can often reset one by slamming it against the floor or some other hard surface. Son slammed it, tested, didn't reset. So we slammed it down again & that did it. I reinstalled it and dryer has worked ever since. (Since this past summer.)

I wasn't averse to getting a new one but it was a case of 'I need the dryer today'. BTW, prices on appliance parts can vary widely so I always check several sources before I order.

ci_lantro,

Thermal fuses work by melting the internal link/circuit at the trigger temperature. That's why they must be replaced. Slamming it to the ground may jiggle the residue to make contact again but it's no longer reliable as a safety device that will trigger at the proper temperature. You're playing with fire, literally.