Immersion heater problem (thermostat?)

19 May 2004
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United Kingdom
Hi everyone,

It seems that my water heater has stoped working. Well, more specifically, when it turns on (via the timer) sparks come out of the immersion heater and it trips the fuse.

I was wondering then if it is a problem with the thermostat in the immersion heater. My water heater has two immersion heaters (one 14'' horizontal from Heatrae Sadia on the bottom and another horizontal on the top from Redrging).

Now I assume that the problem is with the bottom immersion heater (since sparks come out from there just before the fuse burns) and it could be the thermostat or some electrical problem.

Lets say that I change the thermostat. I saw a nice tutorial on how to do that, however, my immersion heater is horizontal and I was wondering do I need to drain the water tank before I attempt to remove the thermostat?

I dont want to flood the place

Please let me know.

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yes you will have to drain it, but not for a stat.

the stat sits within a "sleave"

i would be inclined to suggest its the element that has gone
Normally the thermostat slides out of a tube in the middle of the immersion heater. Sparks indicate a bad connection though, correct or otherwise. The heater is likely to be shorting between live and earth. If you need to remove it yes you will have to drain the tank.
So let me get this straight,

If I need to remove the thermostat I DONT need to drain but if I need to remove the whole immersive heater I NEED to drain.

Is that correct?

I do apologise for the persistence :LOL:
but I am a newbie in these things after all.

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You are correct.

The regulations have recently changed, and the thermostat should be a non-self-resetting type. ie, if it trips you have to press a button before the power is applied. Sometimes the thermostat will not fit in the space allowed in the existing heater, and the heater needs replacing. If your heater is more than 5 years old, and is used every day, change it anyway, it has done well.
Have a look here The picture at the bottom shows you what you are looking at. You can remove the thermostat by disconnecting the wires (AFTER YOU'VE TURNED THE POWER OFF) and withdrawing it.

It is 99% probable that the element has gone though. They tend to corrode over time, water gets in and you get the result you are experiencing now. Oilman is quite right.

You'll need to buy/borrow an immersion heater spanner to get the heater out. It's a fairly straightforward job.

Actually it was that the brown wire from the thermostat had burned and it was touching the metal on which the earth was connected. In other words the earth and live from the thermostat where touching. How strange :)

Anyways, I shielded the brown wire with some electric resistant tape and it works. It is a temporary solution thought, and I should probably replace the white cable that comes from the timer to the water heater.

How do you call these thick white cables by the way? I know that they must be some kind of heat restistant right?

Thank you all for your help.
You can get a high temperature PVC covered cable, but I would use an HOFR (HeatOilFireRetardent) cable.

These cables get hot at the connection on the heater, and should be made long enough for re-terminating. The cable and insulation degrades from the heat, and does not last for ever.
It is 99% probable that the element has gone though.

Oh yes, and the other 1% are due to the insulation of the cable breaking down.


Mr Wise After The Event.

It's always nice to find the problem. :)

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