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(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.