why do heaters always fail in the "on" position?

[Tom R]

Hi Christy

why do heaters always fail in the "on" position?

And while your asking

Why does a stapler always run out of staples right when you need one?

The best way to fail safe a heater system is to use a controller to monitor the temperature and attach all your heaters (cheap or expensive) set to a temperature that is well above that set in the controller. The controller will shut off the electricity to the heater once the controlled heat level has been achieved.

Tom R

[ScubaSteve]

To answer your question... The bimetallic strip activates the switch into the ON position and as it switches over there is often a small arc between the two contacts when they're only a short distance apart. Sometimes this arc can actually cause the contacts to weld together, thus leaving you with a heater that is permanently on. This usually happens as the bimetallic strip begins to fail and the switch switches over slowly or the contacts become worn with age.