It could be a bad manual-reset Thermostat.You could test it by putting it in a glass of warm water...heated to (or add cold water) to near 180F. It shouldn't open.
It may have gone bad from over-use tripping, maybe unknown to previous owner.
You could use a meat thermometer in the vent to test the temperature.With any empty load, timed dry, high heat, it should cycle somewhere between 135F & 160F
I sounds like you already have the Service Manual ?
... I'd think that dunking a switch in water would be come with some kind of "make sure you let it dry out before putting it back in" disclaimer...
...The manual-reset one? If it did, then he wouldn't get any heat until he reset the thermostat.
With any empty load, timed dry, high heat, it should cycle somewhere between 135F & 160F