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.I have tried a heat resisting wire but this burns too as do the plastic top of the thermostats.The fuse is 15amp and has not blown atall during these traumas.The cylinder when connected gets very hot at the top and is often quite cold below.I wonder if anyone can suggest something before I purchase another thermostat .Thanking you ...Skilso