Very Hot Water - Could it be electric immersion faulty?
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DIY Debs
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Very Hot Water - Could it be electric immersion faulty?

by DIY Debs » Sat Jan 17, 2009 4:09 pm

As a mere woman with limited knowledge can any one help with my electric immersion.

Every time I turn it on for more than say 30 minutes the water is so hot it spits and steams out of the taps. Also I noticed when I last used it that it sparked when I turned it off. Is this problem more than the switch, I was wondering if I could buy a new one from a DIY shop and do it myself?

Thanks :D

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by stoneyboy » Sat Jan 17, 2009 9:46 pm

DIY Debs,
Most likely cause is that the thermostat has failed, they are not expensive and easy to replace if there is clearance above the hot water cylinder. If you can find someone locally with limited DIY skills they should be able to replace it for you but note that the thermostats do come in different lengths. If you have a friendly plumber you know it may be easier to get them involved. If you use an unknown plumber a simple job could become very expensive.


by ericmark » Sat Jan 17, 2009 9:57 pm

After the case of the child which died due to an immersion heater over heating and making the header tank so soft it failed and the boiling water killed baby I would be wary of DIY repairs!

Years ago immersion heaters made in the UK had both a thermostat and a non auto resetting over temp switch.

I had to as a child reset ours many times when the Eagle Grate had overheated the water back in the days when kettle was always on corner of stove.

But then we started to get cheap imports and one way to make them cheaper was to omit the safety cut out.

On the old one we had the thermostat was fitted in a pocket (long tube with sealed end) under the immersion heater access plate and this also exposed the live cables.

Which brings me to next point "Can I do it" well I will need a crystal ball there is no way I can assess your ability. But you will be accessing live wires and you should take necessary precautions. I think a good one would be to switch off!

For it to not have tripped the resettable trip I would think you need to have at least the thermostat replaced.

Only two wires but an electrician will also test everything at same time.

I know what I would do. I replaced cistern with instant heat gas boiler but up to you which way you go?

Let us know what you decide.

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by singer » Sat Jan 17, 2009 10:23 pm

Hi DIY Debs

Congratulations first of all for calling it an immersion heater.
Most "mere women" refer to it as their emergency heater which always gets a smile!!

Sparking is caused by load (3KW)if it only occurs when switching off, so no need to worry about it.

Sounds like your thermostat has shorted causing immersion to stay on after water has reached required temperature even allowing it to boil - not a safe situation.

As eric says not really a job for a DIYer.
Call somebody in!!

DIY Debs
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Joined: Sat Jan 17, 2009 4:03 pm

Immersion problem

by DIY Debs » Sun Jan 18, 2009 8:01 am

I think I will leave it for the professionals. Thanks for your answer


by ericmark » Sun Jan 18, 2009 9:37 am

I found this report which may be of interest. ... n%2008.pdf
On checking web sites it seems the extra bit to switch off system if the thermostat fails is all built into one unit these have just two wires and in the main come in three lengths.
There are two types the non resettable which would be used where the immersion heater is sole means of water heating as if the thermostat fails once you would want to replace anyway.
There is also a resettable one for where two or more methods of heating are used one does not want to dispose of thermostat if fail is due to central heating or back boiler.
When the boiler boiled the water in my parents house there was such a noise you knew about it well before the steel header tank got hot and you simply run off hot water in the main to stop boiler being damaged.
In spite of moving dampers when baking it was common for the water to over heat with the old Eagle stove.
You still see ray burns used today.
The thermostat are cheap under £10 but it does require electrical connection.

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