Having just spent the weekend replacing the hot water cylinder,
immersion heater and thermostat - it was all working lovely last night
and this morning, but I've just come in from work to discover the
thermostat has tripped and I've had to reset it.

Why does this trip exactly? The thermostat is set to it's maximum
setting on the dial, so surely it's impossible to set the thermostat
too high?

Under stand it trips because it gets past it's maximum temperature -
although I thought the themostat measured the temperature from the tip
of the device, not the top of it - and the idea was to stop the heater
being stuck on should the thermostat fail on......yet it seems to be
this saftey thing that causes the problem!

This is the second thermostat that's done this and it's going to get
bloody annoying if I have to constantly keep checking the immersion
heater has come on when I get up or get in from work.

I know it's supposedly safer to have this rest thing, but the old
thermostat had been in the tank for the many years without the tank
'exploding' or whatever it's supposed to do if the heater is left on.

Starting to thing a surface mounted thermostat that sits on the outside
of the tank would be better.