Immersion heaters 3 blown in two days!

[magicno1]

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

 

[AlexGas]

Sparkies will tell you more.

 

[dancinplumba]

Possibl voltage surge ?

 

[magicno1]

A surge possible yeh but I've never had this in 31 years has anybody???

 

[dave1]

Possibl voltage surge ?

I was thinking that, what could cause that tho?

 

[dave1]

Maybe someone should take this over to the dark side (sparky forum) who's brave enough? Ha ha

 

[magicno1]

God knows! What the hell would rip apart a titanium heater in under 24 hrs????

 

[SimonG]

The immersions that are supplied with the cylinder are only rated for domestic use. If they are in a commercial environment then they need to be upgraded.

Amazing what you read on a rm label

Dont mention where you have installed it.

 

[gasmanrob]

Just going to throw it out there you are connecting to the right side of the stat if I remember rightly the immersions fitted as standard have external overheat stats. Not insulting you just clearing the obvious

 

[magicno1]

They have co therm stas. Yes connected correctly live to A and neu to B.
no problem you have to ask I know ,
cheers

 

[magicno1]

The immersions that are supplied with the cylinder are only rated for domestic use. If they are in a commercial environment then they need to be upgraded.

Amazing what you read on a rm label

Dont mention where you have installed it.

They are titanium!

 

[efficiencyman]

Might be worthwhile to have the sparks fit voltage optimisation unit if they will pay for one, will save them pounds in the long run if they have regular overvoltage

 

[AlexGas]

Hi
One thing is that the voltage today at 5 o'clock was 251 volts permissible apparently at 253!

You are not wrong here, just looked in the 17th. From 1 January 1995 nominal voltage should be 230V with permitted tolerance of +10%/-6%, which gives us permitted voltage range 216.2 – 253.0V

 

[magicno1]

Indeed
an optimiser has been mentioned but would that extra voltage kill,them?
have to wait and see what the RM guys have to say I guess can't keep spending 200 quid every bloody two days can I!!!!

 

[AlexGas]

Indeed
... but would that extra voltage kill,them?

It should not, cos nothing wrong with 253V.

 

[dancinplumba]

Does it coincide with other electrical items being switched on or off ? Neutral earth fault could cause high current flow thru heaters ?

 

[magicno1]

Could be but the sparks pretty bang on and I'm sure he would of tested that. He had meters and meggers and all sorts of gear up there earlier testing so I'll assume that's ok!
ill double check,of course

 

[AlexGas]

Could be but the sparks pretty bang on and I'm sure he would of tested that. He had meters and meggers and all sorts of gear up there earlier testing so I'll assume that's ok!
ill double check,of course

Have you seen this? The book says: If any sterilisation liquid is in the cylinder do not operate the immersion heater/s as this will cause premature failure.

 

[efficiencyman]

Does it coincide with other electrical items being switched on or off ? Neutral earth fault could cause high current flow thru heaters ?

simple answer NO but the voltage at 251 will make the element burn hotter & shorten it`s life,
On removing the element check for signs of overheating but they should last longer, also what temp was the stat set at did the High Limit trip or not ?

 

[dancinplumba]

Simple answer NO to WHAT ?

 

[magicno1]

Sterilisation liquid????

each time the stats fail. Never trip on the overheat tho!!!! We have about 6 stats by the tank now all :nono:!!!!

 

[Dotty]

Please don't swear magicno1

 

[efficiencyman]

Does it coincide with other electrical items being switched on or off ? Neutral earth fault could cause high current flow thru heaters ?

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.

 

[magicno1]

Please don't swear magicno1

Oops!!!!!! Excuse me!

 

[AWheating]

250v should be fine for an immersion heater and within its designed limits.

 

[magicno1]

Hard water??????

 

[zzzjim]

Have you had street lights in area re-furbed recently ?
( 3 phase is funny stuff when it gets out of balance )

Parents had an electric kiln , is getting it on a different supply an option ?

 

[efficiencyman]

250v should be fine for an immersion heater and within its designed limits.

I agree with that upto a sceptical ( should ) I have had to change hundreds some years have I been supplied with a bad batch ? I have asked that a few times.
Regards Hard Water No not in 24 hours

 

[magicno1]

Not sure re the lights but will ask.
regards faulty batch possible but in my opinion pretty unlikely
will pose the question re three phase!
thanks

 

[magicno1]

Gotta pop out on a call so I'll pick it up later so keep your thoughts coming please!

 

[dancinplumba]

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.

How do you know ? Are you on the job ?

 

[efficiencyman]

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]

How do you know ? Are you on the job ?

Nah Mate, retired now but loved my job.
Experience counts for a lot, learn something everyday can`t get out of the habit even now, just have a bit more time.

 

[magicno1]

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

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

 

[Ch4 plumbing]

I've no experience of water softeners, have they got one and could that be affecting things?

 

[magicno1]

No softener

 

[zzzjim]

Do electrics look any good ( earth bonding of at least some ? )

 

[Chalked]

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.

 

[efficiencyman]

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.

 

[magicno1]

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.

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

 

[magicno1]

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!!!!

 

[turnpin]

Do love an update...will no doubt help someone down the line when you finally resolve this....regards Turnpinunk:

 

[magicno1]

Do love an update...will no doubt help someone down the line when you finally resolve this....regards Turnpinunk:

Pleasure

 

[stani]

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.

 

[chris watkins]

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.

 

[stani]

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

 

[chris watkins]

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

Yes, realised what I put. DOL. but what I think I was getting at is the break down of the insulating powder failure.

 

[stani]

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.

 

[newcastle phill]

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

 

[stani]

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.