Immersion heaters 3 blown in two days!

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Immersion heaters 3 blown in two days!

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magicno1

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Hi
I installed an RM 180 lt direct unvented 2 months ago. It serves a deli and kitchen area so the elements are on 24/7.
Saturday both elements faied and took the rcd. Both were blown as you would expect after say a year or so. Spoke to RM and they advised fitting titanium elements due to heavy constant use so replaced them both yesterday around 3 pm. 11 o'clock today the shop rings no hot water! Drained tank off to find both elements blown apart again!
The electrician is testing the electrics and they all are fine, correct wiring etc! One thing is that the voltage today at 5 o'clock was 251 volts permissible apparently at 253! Could it be over voltage causing this in such short time or crappy elements do you think????? I believe the heaters to be fine and there must be some underlying issue electrically!
We are speaking to RM in the morning if their tech guy answers the phone!!!

any ideas guys please we are stumped.
yes I am cert unvented!
cheers

chris
 
efficiencyman said:
Simple answer NO to both !
As your sparks would have tested for N - E faults The only case I have had like this in 50+ years was on a 3 phase site where 415 volts was found due to a bad install !
It happened at time of colour harmonisation, Blue instead of black when the blue was a phase colour.
Click to expand...
How do you know ? Are you on the job ?
 
Let us know mode of failure, usually gives good clues as to why they have failed in such a short time. Titanium, incaloy or cheapo rubbish, ???? signs of element burn out ?
That 3 phase case I had was a 415 volt wiring mistake ( not mine ) but found it wired like that by original installers.
Ask your sparks to check for any doggy connections or possibility of 415 volts
 
efficiencyman said:
Let us know mode of failure, usually gives good clues as to why they have failed in such a short time. Titanium, incaloy or cheapo rubbish, ???? signs of element burn out ?
That 3 phase case I had was a 415 volt wiring mistake ( not mine ) but found it wired like that by original installers.
Ask your sparks to check for any doggy connections or possibility of 415 volts
Click to expand...


Fitted two two new titanium yesterday. Both set at 50 degrees at 3pm.
both blown today at 11am. Bottom one blew the rcd and the stat but not the overheat. Element was split and burst nearly all the way around.
top one split stat gone but didn't take the rcd or overheat!
previous original heaters two months old incalloy both set roughly the same both shot to pieces again although the bottom one took the rcd and stat but the top one didn't take the rcd just the stat but both never went out on overheat!

previous to fitting this tank they had a megaflo and we were forever changing the elements!
also a lot of the plumbing is plastic barrier pipe connected to copper and I have lost count of the leaks I've fixed there. The copper seems to be corroding in the speedfit joints almost crumbling away.
Do you think this could be related?????
i didn't do the original plumbing it was done about 6 years ago
 
I've no experience of water softeners, have they got one and could that be affecting things?
 
Interesting one this!
please keep us informed how you get on.

out of interest, has the property got a wire type damp proof course? Came across one years ago that was touching the oil line behind an aga. It was shorting down the oil line and where a price of plastic coating on the 10mm copper line was damaged the copper turned to dust.
 
The short life failures seems like an over voltage intermittent fault or a faulty batch.
Regards the previous problems you describe Galvanic action over a period could be a possibility but not the recent blow outs.
Yes, I think the crumbling copper is related to this, I would cross bond all pipe work to cylinder before fitting new elements, to rule out galvanic action.
Interesting one this, I will follow thread !
please keep us informed how you get on.
 
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efficiencyman said:
The short life failures seems like an over voltage intermittent fault or a faulty batch.
Regards the previous problems you describe Galvanic action over a period could be a possibility but not the recent blow outs.
Yes, I think the crumbling copper is related to this, I would cross bond all pipe work to cylinder before fitting new elements, to rule out galvanic action.
Interesting one this, I will follow thread !
please keep us informed how you get on.
Click to expand...

Thanks for all your help and ideas. Back to it today to try to get to the bottom of it!
 
Ok

talked to RM and Rodstat who make the heaters today.
still really none the wiser but they are sending out two replacement elements and want the damaged ones back. They think it could be a faulty batch but unlikely!
we are going to run both elements together and wire them through a timer to limit their usage through the night.
This I know doesn't address the electrical issue but we have to start somewhere. The sparks are putting in a monitor of some description to see what happens over 25 hr period.

if they both blow again within say 2- 3 days back to the drawing board!!!!
 
Do love an update...will no doubt help someone down the line when you finally resolve this....regards Turnpin:punk:
 
If your getting 251volts at peak period for demand I.e. 5 o,clock I would be looking to a serious over voltage during the over night off peak period, if the monitoring cannot show up. The voltage overnight I would be looking at bringing your energy suppliers in to investigate.
 
My two bobs worth, in my experience the main cause of immersions blowing is localised overheating. In hard water areas this is normally due to the build-up of scale, not directly on the elements themselves, although this can happen, it tends to break off the surface and falls to builds up in piles under the elements obstructing the conversion currents which carry away the heat & stop it from overheating.

I use to see these pyramids of scale left in tack by the last engineer as I replaced the element shortly after the new one had been replaced. Use a scrapper to move it way or clear it out before installing new ones.

I though it was a good candidate for the cause of failure in this case until you said that the "top one" had gone as well, if the unit has a higher level "boost" immersion & this has failed as well then that blows my theory out of the water, excuses the pun!

Does the system have a secondary return installed with the mixed system pipework ??

Seems unlikely to be over voltage, when you think you test them at 500+, now measuring the resistance of the new ones may provide useful information.
 
Chris, do you mean test at 500 as in insulation resistance, these are not made to work at that voltage, only that the insulation is still intact, and you wouldn't really test the equipment at 500v
 
stani said:
Chris, do you mean test at 500 as in insulation resistance, these are not made to work at that voltage, only that the insulation is still intact, and you wouldn't really test the equipment at 500v
Click to expand...
Yes, realised what I put. DOL. but what I think I was getting at is the break down of the insulating powder failure.
 
Yes, see what you mean, it will be good to get a definitive answer on this one, especially if they are going through so many.
 
Well an insulation tester does indeed test at 500v.
Mine tests at 500 and 1000v - and those are industry standard tests.
You need the potential across to discover faults in the insulation between the earthed case and current carrying element. These faults may not show at 220v and do manifest at higher.
There are only micro amps during these tests and they are perfectly acceptable on class 1 equipment and indeed obligatory.
You only test at 250v on items with surge protected devices
 
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Phil, are you saying you would test for insulation resistance with equipment fitted I.e. A shower or you would test a boiler circuit with the boiler connected.
 
Im saying id meg the element before fitting.
Whose on about shower or boiler circuits :)
 
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Sorry, didn't read like that thought you were saying you would test the whole lot. I agree testing the jacket to element will show up if there is a fault.
 
Hi

regards secondary circ then yes we do have it. In fact most of the copper pipe leaks have been on the secondary loop!!!!
although the tank in question is 2 months old there is a small amount of scale build up in the bottom of the tank but not huge amounts.
2 new elements arrived today and were fitted by me earlier. The sparks have just text to say they have just wired them in but they are not convinced they are both working!!!!!..... Strange coz they are brand new!!
anyway he's taking a look tomorrow and will let me know ASAP.

also the elements are made by heatrod.
 
chris watkins said:
My two bobs worth, in my experience the main cause of immersions blowing is localised overheating. In hard water areas this is normally due to the build-up of scale, not directly on the elements themselves, although this can happen, it tends to break off the surface and falls to builds up in piles under the elements obstructing the conversion currents which carry away the heat & stop it from overheating.

I use to see these pyramids of scale left in tack by the last engineer as I replaced the element shortly after the new one had been replaced. Use a scrapper to move it way or clear it out before installing new ones.

I though it was a good candidate for the cause of failure in this case until you said that the "top one" had gone as well, if the unit has a higher level "boost" immersion & this has failed as well then that blows my theory out of the water, excuses the pun!

Does the system have a secondary return installed with the mixed system pipework ??

Seems unlikely to be over voltage, when you think you test them at 500+, now measuring the resistance of the new ones may provide useful information.
Click to expand...

Thanks mate

both elements were on 24/7. I understand the scale theory but still the higher one blew!
 
Well done for putting the voltage logger!Also you can connect two elements in series, than you would have ~1/4 power, but double the voltage tolerance.Or go for larger element, and connect it through the silicon diode (would halve it's power).Or find twice as powerful 415V version of it, that would fit in the hole. Should just give the right power at 250V.Anyway, you need something with a lot of thermal headroom... (or good overvoltage protector).Obviously fixing the fault is the best, but if the neighbors are arc welding with 500A+ on the other phase of the 75 KW substation transformer it may not quite help...
 
Is there any chance that the cylinder is being drained, or partially drained.

If the top element has blown, it may be worth checking if the water supply is adequate to keep the tanks filled during peak water usage periods.

The elements don't have to be dry for very long to cook themselves.
 
Update!!!!!

fitted 2 new heaters a week ago on timers and turned off 2nd circ. all ok at the moment touch wood!!!!
RM have the blown elements so we'll see what they say after the break!
 
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