Neutral wire keeps melting - immersion heater

Hi,

the neutral wire on my immersion heater has melted about 5 times in the last year. I've had the thermostat changed twice but the same thing keeps happening.

the thermostat has a reset and is set to 60 degrees. The boost (thankfully) has been okay as I use it very rarely.

everytime I tell my electrician about the problem he spends about 5 mins rewiring then says it should be fine and that there's not much else we can do but keep an eye on it. He said last time he had used heat resistant wire and extra thick - I think 2.5mm? I'm not technical so I'm not sure.

Anyway the problem still hasn't gone away and I'm sick of just ringing the electrician every other month so come and sort and the problem doesn't seem to be getting fixed. 

If anyone has any advice of what the problem could be and how it could be rectified that would be much appreciated! 

I has this once. The only cure was change the immersion heater. It was some kind of internal fault within the heating element itself.

Get the electrician to check how much current the heating element is drawing.

Where is the cable actually getting damaged?

Murdoch said:

Where is the cable actually getting damaged?

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Near the screw 

Sarahabarth said:

Near the screw 

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So so the installation has been done poorly ..... it’s not the cable or the immersion

Is that the screw on the element  ...in the top of the heater  or the screw in switch on the wall ?   

Either way  it must be a poor connection  .     

So it's the screw that the neutral wire is attached to on the immersion heater, not one the wall.  It's got so hot that it's melted through one of the brown wires and charred the side of the thermostat. 

As I said before, I had this once.

The connection was properly made with high temperature flex.

When I was called back for the second time to fix it, I did some more investigating. I re made the connection and turned the heater on and waited.  In about 30 minutes, the neutral terminal was too hot to touch and you could feel the insulation softening.  It was NOT a bad connection.

I concluded it was either a poor connection inside the element getting hot, or perhaps the actual heating part of the element extended too far towards the terminal.  Without cutting it apart you would never know. Replacing the element was the only fix.

I suggest your electrician does the same test.

The current consumed was correct for the power of the heater.

Have seen this a few times... Why is it always the neutral wire that overheats though, and not the line??

apprentice87 said:

Have seen this a few times... Why is it always the neutral wire that overheats though, and not the line??

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On immersion heaters? 

Sure I've seen a few with melted lives/lines/hots whatever....

Yep, just the neutrals on immersion heaters...

john..

The element must be conducting too much heat  up to the terminals  .....as Dave says ...sounds like  a change of heater . 

Thanks for everyone's comments, they've been really useful.  So when you say change the heater you mean to replace the immersion heater part rather than replace the whole boiler? 

yes, immersion element, however it might not come out or rip the tank on its way out so itll be either put up with it not working correctly, or a new tank required

Yes  .  By boiler , I presume you mean the hot water cylinder ?   

It unscrews and can be replaced ,  not expensive to buy ,  best to get a plumber to do it  as sometimes there can be problems not all electricians are geared up for . 

Just as an after thought ....does your  hot water get get boiling hot  ?  Does the  cylinder start sounding like a boiling kettle ? 

Thank you, yes that's what I meant.

No to be honest it's the opposite. Ever since I had a timer installed and started having issues the water doesn't warm up really hot unless I use the boost switch. 

Sarahabarth said:

Thank you, yes that's what I meant.

No to be honest it's the opposite. Ever since I had a timer installed and started having issues the water doesn't warm up really hot unless I use the boost switch. 

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Hum .................... that's an interesting comment. 

Murdoch said:

Hum .................... that's an interesting comment. 

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I think it might be because the electrician set the timings to auto so it only comes on for 4 hours a night - 1am - 5am. I could change this but I find it easier to just use the boost when I want really hot water 

Do you get Economy 7  during the night  then ?  

And did the melting neutral coincide with the new time switch ? 

Just a thought ....do you have gas central heating  ?  And does it also heat up the cylinder?