"Set Square" wrote in message ...

Surely , it would be safer for the secondary device to be *non*-resettable?!

Hmmm, yes. I don't know the logic behind this. It might be that the
device could be tripped by a another fault, say the thermostat being
incorrectly wired or having been removed from the immersion heater
pocket. If the secondary thermostat has tripped it wouldn't
necessarily follow that the primary thermostat is defective, although
that would be the most likely cause.

When you say the older pattern can still be sold, does this have a
non-resettable secondary device, or doesn't it have one at all?

They don't have one at all, only the primary control thermostat. I
think the older type can still be bought and fitted. I believe the
legislation was rushed through and there are still stocks of the old
type in the distribution system.