skilso wrote:

Recently a plumber changed our immersion heater and after being called
back twice to rectify afailed thermostat he embarked on other work
nearer home and I ended up changing the thermostat myself.I have now
changed it three times and each time the same problem arose.even though
the thermostat is set to a low temperature the water overheats and the
power wire to the thermostat melts and eventually disconnects.

Are you sure you have the correct connections?
From my recollection it is easy to make a mistake.

--
Timothy Murphy
e-mail (80k only): tim /at/ birdsnest.maths.tcd.ie
tel: +353-86-2336090, +353-1-2842366
s-mail: School of Mathematics, Trinity College, Dublin 2, Ireland