DIY Doctor

Testing immersion heater THermostat

Postby andrew-webber » Mon Nov 17, 2008 11:54 am

Hi There - I wonder if someone could please help me, or point in the the right direction.

I have recently moved into a new property and the immersion heater is not working, in that it does not heat any water in the cylinder at all. I have left it on for 2 hours and the water is still cold.

I have put one of those mains tester screwdrivers onto the live feed from the switch that goes into one side of the thermostat and it lights up, so the switch must OK, I presume.

I then placed the mains tester screwdriver on the other side of the thermostat and it also lit up again.

Can I assume from this that the thermostat is OK and it must be the actual heater element that is not working, as there was voltage on both sides of the thermostat?

The system must be over 25 years old as the hot water cylinder has no lagging!!

I have brought a replacement 27" immersion heater, but after doing some reading, I am a bit apprehensive about getting the old one out, in case I damage the tank!!
I thus though that I might just get away with replacing the thermostat, but I think that if there is voltage on both terminals of the thermostat then it must be supplying power to the heating element ok?

Many thanks for any suggestions.

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Simply Build It

Postby ericmark » Mon Nov 17, 2008 10:17 pm

With the age I would expect to find a faulty element rather than thermostat although there are other things that can go wrong.
Your screw driver tester is not really good enough to test with and I would suggest that it may be work while getting someone in to do the job.
As you say very easy to rip a tank.

Postby andrew-webber » Tue Nov 18, 2008 1:17 pm

Many thanks for the suggestion - I think that I might get someone in to replace it as the more I read about the possibility of damaging the tank, the more apprehensive I am about doing it!!

Does anyone know what sort of charge I can expect if I get someone in to replace it for me?

Thanks Again
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