New flat immersion heater melting wires

[SamJames]

I moved into a new build flat in July 15 and have had repeated issues with my immersion heater which have stumped electricians. Would really appreciate a second opinion.

I have a cylinder in an airing cupboard with an immersion heater at the bottom which is the only source of hot water (no gas in the building). The immersion heater cable is connected to a DP spur with an analogue timer 15cm above. The timer is set to an hour in the morning and 2 hours in the evening. In Dec the circuit breaker to the immersion heater tripped. An electrician (from Checkatrade) came and found the fused spur had blown (photo attached). He replaced the spur, thinking it was just a one off. A month later and the same thing happened again so this time he replaced it with a "heavier duty" spur which looks like minus the fuse to me. He also took a closer look at the cabling between the timer and the spur and found it was 1mm^2 5 core so replaced it with 2.5mm^2 5 core. He said that this was the fault and it would not happen again.

Fast forward another month and this time the wiring behind the timer melted and damaged the timer (photo attached). This is the short bit of cable the electrician had replaced.

I called another electrician this time and he said it may have been a poor connection though he couldn't tell as it had all melted. He replaced the timer and cabling with 3 core 2.5mm^2 as he wasn't convinced the previous electrician had used heat resistant cabling. He also replaced the immersion heater thermostat (Backer BT7) with one that has a reset (Backer BMST7). He checked both thermostats and did not find a fault with either but as a precaution turned the temperature down on the new one. Now the hot water only reaches about 40C but is only one division away from max in the thermostat.

I would like to turn the temp up but obviously am worried about the same issue happening again as no one has actually identified the fault. The building developers have so far shunned any responsibility despite the electrician saying all flats need to be checked for safety. Would really appreciate hearing any input as to what I should do.

 

[picasso]

Get another electrician to check how many amps your immersion heater is drawing.

 

[Echo the husky]

There is no way on earth the wire stubs attached to that double pole switch are 2.5mm².

Is the thermostat switching off? or is the timer switching off before the water has had time to heat up? If the thermostat is switching off too soon, turn it up a bit and try again. There was a batch of 7" stats last year that had a maximum temperature that was uselessly low, the manufacturer has now sorted the problem and the newer stats of the same model work correctly.

Has anyone measured the current drawn by the element? Should be around 12-13 amps.

The usual cause of overheating is poor installation.

 

[SamJames]

Thank you for the fast replies. The wire stubs in the first photo are from the 1mm^2 cabling that the first electrician replaced with 2.5mm.

After the second electrician turned the thermostat down, I left the timer on for a few hours on his advice to check the temperature and it reached a max of 40C so I think it is the thermostat that is switching off. The second electrician did check the current drawn by the element and said it was fine though I don't recall what the value was. I will double check with him.

Was there a batch number that I could check to see if I have one of the thermostats that were set too low?

 

[endecotp]

Reading your whole post, it sounds like your most recent electrician may have fixed it properly apart from the water not getting very hot. This is quite possibly because you only have it on for a short time. Try leaving it on for several hours and see what happens. If the tank is well insulated, as modern ones normally are, it will be efficient even if on for long periods; the main reason for having the timer would be to coincide with cheap economy-7 electricity periods.

Edit - posts overlapped....

 

[Echo the husky]

I don't know of a batch number but we had several call backs the next day as water only warm. The stats were marked Cotherm. As yours isn't set at maximum yet you can still turn it up and try again.

Edit, I see yours is branded Backer which was not affected.

 

[flameport]

You need to turn the thermostat up to at least 60C, at lower temperatures dangerous bacteria can form in the water.

 

[Echo the husky]

The wire stubs in the first photo are from the 1mm^2 cabling that the first electrician replaced with 2.5mm.

That would explain it!

He also took a closer look at the cabling between the timer and the spur and found it was 1mm^2 5 core so replaced it with 2.5mm^2 5 core.

I've just read this again, how the hell didn't the electrician notice the cable from the spur was 1mm² when he was wiring it into the new spur? I could see it from a small photo! And what moron used 1mm² flex in the first place?!

I called another electrician this time and he said it may have been a poor connection though he couldn't tell as it had all melted.

It looks like the terminal that had melted was the neutral, the 2 wires being neutral in and neutral out, almost certainly a poor connection.

...He also replaced the immersion heater thermostat (Backer BT7) with one that has a reset (Backer BMST7).

If this is a new installation the element should already have an overheat cutout, the newer Backer elements have a separate cutout with white wires and a little black reset button, and so are supplied with rod stats without overheat protection.

He checked both thermostats and did not find a fault with either but as a precaution turned the temperature down on the new one. Now the hot water only reaches about 40C but is only one division away from max in the thermostat.

You will be fine turning it up a bit, (anticlockwise to increase temperature on these) they are supplied sealed at one mark away from maximum, which seems to be ok for most installations. These stats are not very accurate, which is why there are no temperatures marked on them, it's just trial and error to get it right. Make sure the power is off before you remove the cover to adjust though!

I would like to turn the temp up but obviously am worried about the same issue happening again as no one has actually identified the fault. The building developers have so far shunned any responsibility despite the electrician saying all flats need to be checked for safety. Would really appreciate hearing any input as to what I should do.

Turning the temperature up will not melt the wiring. The building developers should be sorting this out for you.

 

[BigSnoopy01]

the builder should be sorting this out. Dont take no for an answer. It seems strange you got an imm with a stat that did not have a cut out, this is against the regs and should not have been fitted. Get hold of your electrical test cert and contact the electrician who wired and tested the house and get them back to check things out, they wired it dangerously with the wrong sized cable and probably a really bad quality switch afterall.

 

[SamJames]

Thank you all so much for all your advice. It's been really helpful.

I've just read this again, how the hell didn't the electrician notice the cable from the spur was 1mm² when he was wiring it into the new spur? I could see it from a small photo! And what moron used 1mm² flex in the first place?!

It looks like the terminal that had melted was the neutral, the 2 wires being neutral in and neutral out, almost certainly a poor connection.

Tell me about it! Two bad electricians but at least I know a good one now.

You will be fine turning it up a bit, (anticlockwise to increase temperature on these) they are supplied sealed at one mark away from maximum, which seems to be ok for most installations. These stats are not very accurate, which is why there are no temperatures marked on them, it's just trial and error to get it right. Make sure the power is off before you remove the cover to adjust though!

Would it be fine to turn it up to the maximum mark? It's on the penultimate mark but only at 40 degrees. I'd have thought it wouldn't be a 25 degree difference between 2 marks.

The building developers should be sorting this out for you.

I will keep applying pressure on the developers. Is there anyone I could report them to if the developers refuse to take any action? I am obviously concerned as the whole building is likely to have the same wiring issues as ours flat. The electrician suggested reporting it to the citizens advice bureau/trading standards. I don't particularly want to go down this route.

 

[Agile]

You talk about the "whole building" a if its nothing to do with you.

Almost certainly al the flats have the same problem.

Usually those living in new blocks communicate with each other an many firm a residents association or similar.

You all need to join together in dealing with the developers.

They are meant to provide a guaranty.

Tony

 

[BigSnoopy01]

you should have guarantees with the builder both for a limited time for such things as plumbing and electrical and for 10years on structual. Even if the guarantee period has gone a company is still liable for work done that was done incorrectly or unsafely. For example if a plumber fits a tank overhanging the tank stand and it fails 5 years later its still the plumbers fault for incorreclty fitting the tank, if it was fitted correctly and it failed it would not be the plumbers fault.

you should have some guarantee details in your hand over pack, the electricians will be a member of an approved body which can be contacted to make a complaint. The builder will have used local building control authority or someone like the nhbc which can be contacted to report issue, they will probably be interested if all the flats have undersized cables and are a fire risk.

 

[Agile]

All very good except that the NHRBC is only to cover serious defects like subsidence.

So they have a minimum claim level and that is probably in the order of £2000. Unfortunately most wiring problems will be below their minimum figure.

Tony

 

[SamJames]

You talk about the "whole building" a if its nothing to do with you.

Almost certainly al the flats have the same problem.

Tony

I haven't said it isn't anything to do with me. I notified the building management (they act on behalf of the developer) as soon as the issue was spotted but so far they've ignored the issue. It's a fairly new block with lots of renters so ideally I would need to get into contact with the landlords. The problem is who to contact if the management don't seem to care.

you should have guarantees with the builder both for a limited time for such things as plumbing and electrical and for 10years on structual. Even if the guarantee period has gone a company is still liable for work done that was done incorrectly or unsafely. For example if a plumber fits a tank overhanging the tank stand and it fails 5 years later its still the plumbers fault for incorreclty fitting the tank, if it was fitted correctly and it failed it would not be the plumbers fault.

you should have some guarantee details in your hand over pack, the electricians will be a member of an approved body which can be contacted to make a complaint. The builder will have used local building control authority or someone like the nhbc which can be contacted to report issue, they will probably be interested if all the flats have undersized cables and are a fire risk.

So unfortunately, it only has a CRL warrantee which is 10 years structural. The wiring inside is not covered and the excess is also £1000. I've argued that this should be covered by a guarantee on the work by the builders but the management are insistent that the guarantee period is over (despite it being less than 6 months since we completed). Is there another body I could report to?

 

[Echo the husky]

If the electrician who did the installation is a member of NICEIC, Elecsa, NAPIT etc. I'm sure they will be interested to know that one of there members is carrying out work that falls far below the minimum standard.