A bit less than a year after replacing all the thermal switches / cutoffs / thermostats in the Whirlpool clothes dryer, the Thermal Cutoff went open-circuit. It’s located at the top of the heater duct:
The wiring diagram lists it as tripping at 350 °F and “NOT RESETTABLE”:
Curiously, the replacement switch had only one mark:
I find it difficult to believe anybody would build a thermal cutout at 309°F = 154 °C.
Crushing it with a Vise-Grip reveals the interior:
I don’t know what permanently opens the circuit in there, but it definitely happened. The contacts remain unblemished, so they were pressed firmly together until the end.
With nothing to lose, I reinstalled the Thermal Cutoff I removed last year (*) and the dryer works fine again.
It is possible lint accumulating in the filter bag I added to the exhaust vent restricted the airflow enough to overheat the cutoff, but the Operating Thermostat should keep the air around 155 °F and the Hi Limit thermostat should have tripped at 250 °F, long before the temperature reached 350°F.
Another cutoff will arrive shortly and will remain in the Box o’ Dryer Parts against future need.
(*) Which is why I keep the old parts around, because a dubious part on hand is much better than the new part I might not be able to get due to, oh, “supply chain issues”.
The Smell of Molten Projects in the Morning 
Spam comments get trashed, so don’t bother. Comment moderation may cause a delay.