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Immersion heater wiring problem

Postby maggienoodles » Sun Dec 26, 2010 1:02 pm


I do not know very much about electrics, some idiot did not change a fuse properly outside our building and instead id a botch job and put some fuse wire to do the job. This then fused on xmas day and we were without power. The fuses in the house were fine, but when we switched the immersion heater isolation switch, it only comes on with the light when the secondary switch in the bathroom is switched off. I have never looked in side this but would this have a thermostat inside the cover? After looking at the picture perhpas this is where the problem stops. Would this oinvolve changing the entire socket i.e. new thermostat or, would it have a fuse that could be changed? Do I need an elctrician to change the socket if that is what is wrong? How do i know this is where the problem is?

This has happened before but after six months of it not working it suddenly started again- i think this ay have been loose connections in the isolating ijmmersion heater switch however.

Any help would be appreciated! Thanks
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Postby ericmark » Sun Dec 26, 2010 10:14 pm

Where two switches are used with immersion heaters unlike lights they are not two way. As isolators they should be wired in series that is both need switching on for it to work but some times they are in parallel that is both need to be off to isolate.

There are many different immersion heater designs. Where a flimsy plastic tank is used in the loft the thermostat has a non re-settable thermal fuse so if it overheats you need to change the whole thermostat. However where solid fuel heating is used the header tank has to be able to stand boiling water and in that case the thermostat has a reset button which can be pressed should the water get too hot.

Willis in Ulster has a really great system where the immersion heater is in a separate tank and heats the cistern from top to bottom instead of bottom to top so you get hot water quicker than the standard mainland type. Who says the Irish are not clever? This system has two thermostats only Irish are clever enough to work that out!

Any loose connection is likely to cause a fire and you seem to have limited ability so may be best to get someone in.
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