In article , Huge
writes
A couple of months ago, the immersion heater overheated and melted both the
insulation
and its plastic cap...

So I assumed the thermostat was faulty, bought and fitted a new one and
fabricated a
new cap from plastic drainpipe.

The new thermostat has an overtemperature trip, which keeps tripping. So,
whatever's
wrong is still wrong. I carefully remade all the joints when I replaced the
thermostat
(I assumed that's what the problem was), so I imagine it can't be that.

Could the element be furred up? We have very hard water and our water softener
packed
up years ago....


Why ever not change the whole thing?. They aren't expensive and chances
are that if its been that hot, its not done the element a power of good
as they don't last that long and the improvised cover, sounds well
improvised.

Bet that theres a partial short from live to earth in the heating
element, so part of the heater is going much hotter than it should.
Shorts in immersion heaters are a regular source of RCD trips.....
--
Tony Sayer