"George Patterson" wrote in message
news:ZJywh.14566$RJ4.928@trnddc08...
KurtG wrote:

How often do these go haywire?

That depends. I used to have heaters made by Supreme. These had, as many
others do, "thermostats" that were metallic expansion segments which
separated a pair of electrical contacts. The general idea is that the
segments will expand as they heat up and force the contacts apart. That
cuts off the power to the heating coils.

These things had a nasty reputation for sticking; almost always in the
"on" position. It became a not-so-fun game to try to replace the
thermostat before it went bad. I replaced my heaters years ago with the
"Tronic" brand, which have an electronic thermostat. I've been told that,
when these fail, they tend to fail in the "off" position. Mine have not
failed in over ten years, but they do seem to need adjustment every few
months these days (they didn't when I first bought them).

Once burned, twice careful, though. I still keep two heaters on my tank.
Each one is about half the size the tank really needs. If one goes
haywire, it's not large enough to really boil anybody. I wouldn't be
adverse to using three, if that's what it takes to keep everyone alive.

The Supremes used to go bad about every three to five years.

George Patterson
No one ever says "It's only a game." when his team is winning.

Another option is to put them on a controller of some sorts. All mine are
plugged into my Reefkeepers or Reefkeeper 2`s. They will operate normally
until it hits its set thermostat setting. If for some reason it sticks on
the Reefkeepers will shut that power plug down at a pre-set temp and shut it
off. I have mine set 2 degrees above the heaters set point. Its like a
double safety switch in case of failure.
I had a friend that had a 200 watt model stick on and it turned his tank
into a cooked marine based soup. Not pretty nor pleasingly aromatic in the
end...