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

[bauder1986]

Originally Posted by christyf5

oh this is some crap brand probably, I don't even think it says on it. It just says Thermo Compact Pre-Set. Its a 50watter so I was kind of limited by what I could find for a nano around here.

Those pre-set temp heaters are dangerous. Had one a while back that cooked my tank and killed off half of what i had.

[christyf5]

Originally Posted by bauder1986

Those pre-set temp heaters are dangerous. Had one a while back that cooked my tank and killed off half of what i had.

this one is no different from any of the other heaters I have, are there some that aren't pre-set (that don't cost a fortune because they have their own fancy external controller)? All of mine you dial to wherever you want it and it heats to that temperature (or close to it anyways).

[fencer]

most heaters are regulated by a bimetallic strip which basically will fail with time. They are not seleniod switches which open on fail. Your best choice ia a Thermocouple and controller. You can program in failsafes