Does my immersion element need replacing?

[Ankle_Deep]

I'd appreciate some guidance on whether my thinking is right:

Direct feed, immersion-only tank, probably about 15 years old.
Lower, side-entry element stopped heating the water at night. Testing showed that the timer was no longer switching the relay, so I replaced it. Since then, it has not been heating the water particularly hot. Checking the new timer suggests it works: clicks on at the right time, can hear noise from the tank.

Thermostat has always been a bit iffy: small change to the temp selector has a bit change in water heat, but it wasn't altered during the timer replacement. Thermowatt RTB Plus

While a thermostat swap is within my capabilities, I suspect that the element is knackered and it was perhaps drawing too much current and knackered the timer. Reasons for thinking this:

RCD tripped on first use of new timer (possibly coincidence)​

Cable to thermostat shows black coating on the copper strands of the live core​

When turned on, the element instantly makes a loud noise: louder than a normal boiling sound.​

I think that the element may be split and so need replacing, but I would appreciate other's opinions since this will require me to get a plumber in to replace it (apartment, so I don't want to risk flooding)

 

[Roy_66]

Do not proceed unless you are qualified and experienced. It's just too easy to make mistakes with electrics. As a friend has just told me (after giving himself a belt today) you can't see the bloody stuff. Just because a shock hasn't killed you doesn't mean no heart damage.

If you aren't sure about the electrics I'd get an electrician in first, in fact before you switch it on again. Does the thermo cable with blackened cores get hot ? (Wiring fault? and/or faulty component perhaps. If old age then it needs changing). The timer should probably just provide a volt free contact. Has anything else changed?

Have you isolated first and proved dead (do you have test equipment for that) and first visually inspected the heater terminals, then disconnected the heater electrically and tested at the terminals? Just an example of sort of fault you might not expect:
IET Forums - Immersion heater and burnt out neutral - https://www2.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=36577

Also how old are the cables and can you change them easily (are all components in same area).

Take care, and only work when fresh and relaxed, and never under pressure.

Remember the immersion is a high power circuit, so more dangerous and you need the electricians skill to get high power terminals tight and without breaking them. They have lots of skills that you and me would not realise, that they apply to each job.

Leave it to a pro?

Cheers,

Roy (Amateur all trades)

 

[Aquarius]

Agree with what Roy has said, you need to prove dead, otherwise you may end up dead or seriously injured. If there’s blackness on the line in on the thermostat, it’s could be that it’s knackered, are you able to test (after dead testing of course) resistance across it? You may also need to perform a live test to ensure correct voltage is being delivered, if you’re not comfortable with any of this, then get a plumber/electrician in.

 

[Bengie]

I would suggest you take into consideration the hardness of the water. If it's hard then
the element is most likely coated so not very efficient.

 

[Ankle_Deep]

If you aren't sure about the electrics I'd get an electrician in first, in fact before you switch it on again. Does the thermo cable with blackened cores get hot ? (Wiring fault? and/or faulty component perhaps. If old age then it needs changing). The timer should probably just provide a volt free contact. Has anything else changed?

Have you isolated first and proved dead (do you have test equipment for that) and first visually inspected the heater terminals, then disconnected the heater electrically and tested at the terminals? Just an example of sort of fault you might not expect:
IET Forums - Immersion heater and burnt out neutral - https://www2.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=36577

Agree with what Roy has said, you need to prove dead, otherwise you may end up dead or seriously injured. If there’s blackness on the line in on the thermostat, it’s could be that it’s knackered, are you able to test (after dead testing of course) resistance across it? You may also need to perform a live test to ensure correct voltage is being delivered, if you’re not comfortable with any of this, then get a plumber/electrician in.

Sorry, I realised that in an effort not to write a massive wall of text to bore you with, I skipped over some of the testing I did and should have mentioned:

I did both live and dead testing and confirmed 100% that the timer was not switching on the supply to the heater (rather than an issue with the cabling or the supply) After the dead testing, I did my customary restripping of the terminal ends (I like clean copper) and discovered the blackened copper: so I replaced all the cable at the same time as replacing the timer.

The problem is definitely either the thermostat or the element itself. My feeling is that the blackened wiring is more likely to be caused by a faulty element, rather than the thermostat, but I am open to expert opinion on that. I haven't done any resistence testing of the element, but I suppose I should do that next?

I would suggest you take into consideration the hardness of the water. If it's hard then
the element is most likely coated so not very efficient.

My water is so hard it comes out of the tap as small rocks and can break a cheap kettle within 6 months. I do have the fear that the bottom third of my tank is a solid lump of limescale.

 

[Murdoch]

Any local spark could easily test the immersion ...

but be very careful fiddling around because you may have a neutral problem ....

 

[Basher]

If you have a multimeter, the high ohms range (between E and L or N) should indicate if there is a major insulation issue with the immersion element (after disconnecting it obviously). As Murdoch says, an electrician with a MFT could and would do this test at 250v or 500v to check it properly.
in my humble opinion it's not terribly likely that the immersion is taking higher current and hence knackered the original timer (that could just be a fault). A common immersion failure mode is corrosion of the sheath resulting in leakage between the element and earth. You say you have an RCD so once leakage reaches over 30mA it should trip. Without an RCD, the current to earth goes up until the fuse goes or MCB trips. That's when it's important to have good earth connections!
I've had calcium build up in the bottom of the tank to the point it reached the lower immersion, which resulted in the immersion packing up. Discovered a huge amount of white silt when I took the immersion out, which I dug out before replacing the element. Your element is hopefully not low enough down for that to occur.
But having said all that, I am suspicious of the behaviour of your immersion thermostat - I would replace that if an insulation resistance test shows no other problem.

 

[townfanjon]

Not read all above .
Its an educated guess the element has blown and taken the timer with it .
Drain down , new element and stat .
I wont dare tell you how I test the element, the sparkies on here will tell me off .

 

[Ankle_Deep]

If you have a multimeter, the high ohms range (between E and L or N) should indicate if there is a major insulation issue with the immersion element (after disconnecting it obviously). As Murdoch says, an electrician with a MFT could and would do this test at 250v or 500v to check it properly.
in my humble opinion it's not terribly likely that the immersion is taking higher current and hence knackered the original timer (that could just be a fault). A common immersion failure mode is corrosion of the sheath resulting in leakage between the element and earth. You say you have an RCD so once leakage reaches over 30mA it should trip. Without an RCD, the current to earth goes up until the fuse goes or MCB trips. That's when it's important to have good earth connections!
I've had calcium build up in the bottom of the tank to the point it reached the lower immersion, which resulted in the immersion packing up. Discovered a huge amount of white silt when I took the immersion out, which I dug out before replacing the element. Your element is hopefully not low enough down for that to occur.
But having said all that, I am suspicious of the behaviour of your immersion thermostat - I would replace that if an insulation resistance test shows no other problem.

I don't know why I said it was an RCD when it is just a simple MCB (brainfart caused by a cold shower?)

1.5K Ω across the element terminals tells me it is knackered: the insulation test seems okay (with my cheap multimeter...), so at least no lumps of electricity are going to fall on me while showering. Guess I am waiting until the plague is over and then getting a plumber to come in and replace the elements (might as well do both at the same time and get longer-lasting ones).

Still, no major hardship - I'll just switch this one off and use the booster instead.

I really appreciate the help you all have given me: some very helpful words of wisdom.