Immersion tripping rcd

[Dustyy]

My aunt has a problem with her immersion tripping the rcd on her consumer unit. The problem has only recently started occurring and occurs even when all other mcb's except the immersion are switched off. I have checked the wiring to ensure all is correct and tight at both the cu and the immersion and all seems to be in order. The rcd trips after about 15secs, and from memory the rating of the rcd was appropriate, but as i day the problem has only recently started occuring. When the immersion mcb is switched off and everything else on the rcd doesn't trip.

Though the current wiring to the immersion looks up to date, some remnants of the old wiring remain at the immersion end (unconnected now) but would possibly indicate that the immersion element is fairly old.

Could a fault in the immersion element be causing the trip? If so how and would a replacement element be the easiest solution.
My aunt is 96 and lives on her own so I don't want her to be 'preyed' on by anybody unscrupulous!

Any ideas greatfully received......

 

[Malc]

I'd say you have almost conclusively proved it is a faulty immersion heater. The only other option might be the cable run to the heater but you could easily check this by disconnecting the immersion at the tank and then trying again. Of course do not leaving the live ends dangling .

I'd suspect corrosion letting water into the heating element. Probably a tiny pin hole. In construction the heating element is a copper tube filled with sand with a bare wire in the middle that gets hot. The sand absorbs water and there is your earth leak.

 

[Dustyy]

Thanks Malc.
With regards checking the immersion and leaving the wires dangling, I will be going to my aunts house tomorrow and will be on my own in the house (therefore no chance of anyone else touching what they shouldn't), at the risk of setting myself up for ridicule here, will the circuit still be complete if the wires are not connected and if there is a fault with the supply wiring would this be detected and trip the rcd?

 

[phhut]

What Malc was saying is that the cable itself might possibly be the cause. If you disconnect the wire at the immersion end, this 'fault' would stay on the cable run, so would trip the RCD - if that was the cause and not the immersion heater.

Mind you it could also be a fault (stray wire strand maybe) inside the terminal block on the immersion so inspect that CAREFULLY before disconnecting.

But, as Malc said - it probably is the immersion element, which you can replace yourself with the aid of a special spanner (available at DIY stores or a plumbers merchant).

 

[the_main_dude]

yes defintly a faulty eliment

 

[ban-all-sheds]

You should probably now trundle over to the plumbers forum (speak slowly for they are hard-of-thinking) and find out tips and pitfalls regarding immersion replacement.

Here's a couple to get you going:

1) A G clamp can be used as an improvised spanner if you don't have, or can't get access to use, a proper one.

2) Take great care to closely observe the tank where the element screws in. If it's stuck, and the tank is old and thin it is possible to tear the tank, and this is a Bad Thing™. A smart tap on the spanner with a hammer can be useful to loosen it without applying a lot of movement, and/or trying to tighten it a tad.

3) And I hate to mention this one lest I offend, but you wouldn't be the first to not do it... don't forget to turn off the cold feed and drain off some of the cylinder first....

 

[Dustyy]

[3) And I hate to mention this one lest I offend, but you wouldn't be the first to not do it... don't forget to turn off the cold feed and drain off some of the cylinder first....

Most obvious can often be easiest over looked in my book so thanks for the reminder

My trusty sledgy is poised for 'tapping'

 

[Malc]

3) And I hate to mention this one lest I offend, but you wouldn't be the first to not do it... don't forget to turn off the cold feed and drain off some of the cylinder first....

Yeah I once made the mistake of answering a question from my mother - re how do I change the toilet cistern washer as it won't stop running - Easy they are all plastic these days. You should be able to change it by hand. So she did - and blamed me for not telling her to turn the water off first . Well she didn't ask that .