"Set Square" wrote in message
...
In an earlier contribution to this discussion,
Aidan wrote:
(Ken Knott) wrote in message
. com... Since you
can
select the temperature using the dial i don't really understand what
resettable means in this context. can anyone explain? thanks.
It has a secondary, manual-reset thermostat, a safety device that
operates at a higher temperature than the first adjustable thermostat.
The contacts on thermostats can often fail by spark-welding themselves
together, so they fail to an unsafe condition. If the re-settable
thermostat operates, it can be reset by pressing a small button. This
is supposed to alert the operator to the fact that the system has
suffered a failure and it needs fixing.
A woman was killed in Cornwall , about a year back, when boiling water
from a defective immersion heater thermostat accumulated in the water
storage tank in the loft. The plastic tank collapsed, sending a
cascade of boiling water through her bedroom ceiling. The relevant BS
was changed after this, but the older pattern, non-resettable, type
can still be sold.
Surely , it would be safer for the secondary device to be
*non*-resettable?!
You can get non resettable versions. As Ed said, the idea is that you need
to remove covers to reset the stat (to stop the plebs messing about). I
understand it is now compulsory to only fit stats with a secondary
(overheat) thermal cut out.
Adam