I have an F100 that works great for a few hours, but then the thermal cutoff blows. I've monitored the temperature with a thermocouple meter connected to the spare pins used for setting the setpoints, and it seems to be working correctly and stays within the desired window. It only seems to fail in use, not on the bench. I believe the thermal cutoff switch is going 'soft' from age and triggering due to bass and vibration (hence it doesn't fail on the bench).
It's possible also that, since the switch is outside the heat exchanger, it's set to trigger at a lower temp than the max temp of the core, and that for some other reason more heat is 'leaking' out of the heat exchanger than normal causing it to trigger.
Does anybody know the rated temperature of that switch? I'd like to monitor the temperature on the outside of the heat exchanger (where the switch is located) to see if maybe it's getting hot (due to bad insulation or something) even if the core temperature is within spec.
Thanks,
Jeff