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

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

In article ,
skilso writes:

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

I wonder if you have a long thermostat and a short element?
Not that I would expect this to cause a wire to melt, but it
could cause the water to be too hot at the top.

--
Andrew Gabriel

If you can obtain a multimeter from someone, check the actual resistance of
your immersion heater element. Make sure that you disconnect all wires from
the heater and thermostat. The resistance of the heater should be about 20
Ohms assuming it is a standard 3kWatt heater. With this same multimeter you
can also check that there is no electrical leakage between the heater and
the copper tank itself. The copper tank should be connected to Earth.


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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.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


What make of thermostat are you installing ?

Try a different brand, which has suitable British Standards markings on.
Also the temperature does not need to be high for a immersion, and often
they are set way too high, around half way or less on screw setting
should be enough.

J

skilso wrote:
Recently a plumber

A sudden thought about this. Is there an open vent pipe from the top of
the cylinder, which terminates over the cold water storage tank?

It might be that sometimes part of the heater and the thermostat are
not immersed in the water. This could explain the melting and why the
cylinder is cooler lower down. It shouldn't be possible for the heater
to become un-immersed, but there are some lunatic installations around.

If there's no open vent, the water level may drop as air accumulates
at the top of the cylinder.

You should be able to find a diagram of the correct cylinder
installation on the web or in a DIY book, to compare with your set-up.

Thankyou to all contributors and I regret I was unable to read them and respond until now .....during this time a different type of thermostat has been fitted and appears to have solved the problem,it seems that the range of new thermostats which I used must have been inferior,So Whilst thanking the other contributors it looks as if John hit the jackpot. Many thanks to you all...... SKILSO