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

 

[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!