Corrosion Ariston Hot Water System

[Tony Holl]

Hi (hope we're in right place - sorry if not - we're new to this) – we
are having serious corrosion/galvanic erosion with our Ariston
Unvented Stainless Steel Hot Water System. We are on our 3rd copper
thermostat tube (£80!) and 3rd immersion element (magnesium
sacrificial anode included - £40) in 18 months.
Ariston have no answers nor do our plumbers (£250!) – just arrived
home to water again leaking from the
thermostat tube!
Can you please put us in touch (via email/telephone...) with anyone
who
might be able to shed some sort of light on a solution/cause of our
problem?.
The house/system is 6 years old – original plumber doesn’t know what
the
problem is. Have noticed a small (200mV) on the earthed pipes joining
steel tank - but can't prove electrolysis is fault.
Thanks in case you can help.
Regards
Tony

[Onetap]

On Nov 6, 4:34 pm, Tony Holl <tonyhol...@gmail.com> wrote:

>  The house/system is 6 years old – original plumber doesn’t know what
> the
>  problem is. Have noticed a small (200mV) on the earthed pipes joining
> steel tank - but can't prove electrolysis is fault.

Defective earth connection? How can you get a voltage from an earthed
pipe, when earth is 0V? It isn't earthed. What are you using as 0V for
the measurement of the PD in the pipe?

Whereabouts are you?

Electolysis is the cause. The currect (!) Arsiton water heaters have
an electronic anti-corrosion device. Maybe you could get one of those.

[tonyh...@gmail.com]

Thanks for the reply. Have checked whole electric system now - it would appear there is 200mV showing across the Service box earth (PME from road) and a "ground rod" which we've buried (banged 2' into) into the ground outside, if you see what I mean. This 200mV shows up throughout the house on earth connections in sockets etc and the new "Earth".

There is however only 20mV showing across new Earth and "Neutral" - ALL power switched off at Service box, of course.Think the 200mV might be coming courtesy EDF? Is it enough for corrosive electrolysis?

The immersion element includes a sacrificial anode on our model - Ariston just said they don't use them anymore, didn't say why! Thanks! Have taken out immersion (sic, anode)and put "blank" in pro-temp - hope the won't make corrosion worse without the anode.

Electronic anti-corrosion device? Will invstigate - but not sure Ariston Technical will be able to help - have you any knowledge/experience? Would be cheaper than the Thermastore we've been looking at online this afternoon!!

Sorry about the long reply - just hoping it makes some sense.

[harry]

On Nov 6, 4:34 pm, Tony Holl <tonyhol...@gmail.com> wrote:

How about getting s stainless steel thermostat tube?
Also there are SS immersion heaters for acidic water areas.
You might want to check the Ph of your water. There are narrow range
litmus papers for this purpose.
The water company normally treats it to make it slightly alkaline to
stop pipe corrosion.

You're not on a well or spring? Spring water is often acid.
Sometimes circulating currents can be limited b putting in a bit of
plastic tube instead of the metal. (How much metal pipework/plastic
have you?)

200mV with respect to what? AC or DC? If AC, there is an electrical
fault, If DC, it's an electrolytic thing) There should be no voltages
appearing on your pipework, it should all be securely earthed. ( It's
possible there is an earth fault nearby) If on your own system, why
hasn't the RCCD (earth trip) operated?

All these things need looking into.

[Onetap]

I believe that sacrificial anodes were stopped being used because the
Water Regulations prohibited their use, or the metal corrosion
products they drop into potable water systems (I've haven't come
across anything that confirmed this). All the unvented water heater
manufacturers started using electronic devices some years (8+??) ago.
I don't know the details, they just make apply a positive charge to
the heater, making it the cathode and protecting it. If you look at
the installation instructions for the recent Ariston water heaters,
they have them fitted.

You need the sacrificial anode, once it has gone the heater casing
starts to corrode.

I'm not an electrician, but the stray earth current sounds wrong
and I'd suspect that would be the cause of your problems. It could
cause corrosion problems.

[Andy Wade]

On 06/11/2011 17:49, tonyh...@gmail.com wrote:
> Thanks for the reply. Have checked whole electric system now - it
> would appear there is 200mV showing across the Service box earth (PME
> from road) and a "ground rod" which we've buried (banged 2' into)
> into the ground outside, if you see what I mean. This 200mV shows up
> throughout the house on earth connections in sockets etc and the new

Such voltages are perfectly normal and are generally of no consequence
whatever. I very very much doubt that they're anything to do with your
corrosion problem.

In the PME (aka TN-C-S) system the earth and neutral conductors in the
street mains and your service cable are one and the same, so voltage
drop along the neutral due to normal load current causes a potential
difference between the supply 'earth' and the local 'ground'. This can
reach several volts - 200 mV is 'nothing'.

> There is however only 20mV showing across new Earth and "Neutral" -
> ALL power switched off at Service box, of course.

Your wiring earth and neutral are bonded at the PME earth terminal in
the supply cut-out (the unit containing EDF's main fuse). On no load
the PD should be zero, but stray earth currents flowing quite normally
in your main bonding conductors could cause such a tiny PD - where
exactly did you put the meter probes?

> might be coming courtesy EDF? Is it enough for corrosive
> electrolysis?

That's highly unlikely, IMO. You're measuring with the meter set to AC
volts, I presume? Try putting the meter on DC - any DC offsets in the
earthing and bonding would be far more likely to drive electrolytic
corrosion, but even than you've have to consider what current path is
relevant to the problem. Do you live near anything that could put
significant DC current into the ground, e.g. LV electric railway,
tramway, telephone exchange?

> The immersion element includes a sacrificial anode on our model -
> Ariston just said they don't use them anymore, didn't say why!

Cost reduction, increased spares sales...?

> Thanks! Have taken out immersion (sic, anode)and put "blank" in
> pro-temp - hope the won't make corrosion worse without the anode.
>
> Electronic anti-corrosion device? Will invstigate - but not sure
> Ariston Technical will be able to help - have you any
> knowledge/experience? Would be cheaper than the Thermastore we've
> been looking at online this afternoon!!

The cylinder is a closed surface, electrically. Faraday sayeth that
there can be no electric field in such a closed vessel, unless it's
introduced somehow. The voltage on the surface relative to earth is
quite irrelevant. To get internal currents there would have to be
internal electrochemical PDs (as there will be with those sacrificial
anodes), or else a PD or current introduced through one of the penetrations.

HTH but I've no more to suggest ATM. I'd continue to badger Ariston.
Your water company might help too - is the pH of your water unusually
high or low?

--
Andy

[Onetap]

On Nov 7, 9:12 am, Andy Wade <spambuc...@maxwell.myzen.co.uk> wrote:

> The cylinder is a closed surface, electrically.  Faraday sayeth that
> there can be no electric field in such a closed vessel, unless it's
> introduced somehow.  The voltage on the surface relative to earth is
> quite irrelevant.  To get internal currents there would have to be
> internal electrochemical PDs (as there will be with those sacrificial
> anodes), or else a PD or current introduced through one of the penetrations.

Eh???

I think you're confusing this with something else.

It is bimettalic (aka Galvanic) corrosion. There are two different
metals (water pipes and cylinder shell) connected and with an
electrolyte. The least-noble metal (usually the steel/SS cylinder)
corrodes. It's to do with a current passing through the water by
hitching on the metal ions. Putting a sacrificial anode in protects
the cylinder shell, so long as the anode is replaced regularly.

[Andy Wade]

On 06/11/2011 18:22, harry wrote:

> 200mV with respect to what?

That's answered in his second post, /quod vide/.

> [...] If AC, there is an electrical fault,

No evidence whatever has been posted to suggest that. What sort of
fault do you think would be relevant?

> [...] There should be no voltages appearing on your pipework, it

> should all be securely earthed.

Oh dear...

1. Pipework, not being part of an electrical installation, cannot
constitute an exposed-conductive-part and therefore does not require
*earthing*. It may however be connected to the means of earthing via
the main or supplementary equipotential *bonding* which is required for
extraneous-conductive-parts. It could also be earthed simply because of
conductive contact with earthed electrical items such as boilers,
heaters, motorised valves, etc., which are earthed via their own circuit
protective conductors. Pipework which is in neither of the latter two
categories can quite happily be left electrically floating.

2. "Earthed" does not imply zero PD to the local soil. In the PME
system there is always some diverted neutral current present in the
ground, since the multiple earthing electrodes are all at slightly
different potentials. Where metal gas & water services are present
there are always similar currents in the bonding conductors (your water
bond, in series with next door's and a section of water main form a loop
in parallel with a section of the mains neutral. Bonding conductors are
sized to carry these currents without problem. The associated voltage
drops due to resistance and reactance mean that small PDs are always
present between different points in the earth net. As I said earlier
this is all normal and inconsequential.

> [...] If on your own system, why hasn't the RCCD (earth trip)
> operated?

There are MCBs, RCCBs and RCBOs, the latter two being types of RCD, but
what, please, is an RCCD?

> All these things need looking into.

I think not.

--
Andy

[Andy Wade]

On 07/11/2011 12:51, Onetap wrote:

> Eh???
> I think you're confusing this with something else.

No, I said "To get internal currents there would have to be internal
electrochemical PDs ,

> It is bimettalic (aka Galvanic) corrosion. There are two different
> metals (water pipes and cylinder shell) connected and with an
> electrolyte. The least-noble metal (usually the steel/SS cylinder)
> corrodes. It's to do with a current passing through the water by
> hitching on the metal ions. Putting a sacrificial anode in protects
> the cylinder shell, so long as the anode is replaced regularly.

Yes, so... (current due to internal electrochemical effects, wot I said).

--
Andy

[Onetap]

On Nov 7, 1:21 pm, Andy Wade <spambuc...@maxwell.myzen.co.uk> wrote:

> No, I said "To get internal currents there would have to be internal
> electrochemical PDs ,

> Yes, so... (current due to internal electrochemical effects, wot I said).

Why say it and confuse the issue? Faraday says A unless B, but B
applies, so we can ignore A and Faraday.

200mV is loads of PD to create a corrosion issue. I'm fairly sure that
you couldn't produce that sort of voltage with mains water in a
corrosion cell.

[tonyh...@gmail.com]

Called EDF out today and they have confirmed that their PME earth impedance reads 0.28 ohms - right in the middle, they said, of the permitable limits. So not them, then.

Now what I'm seeing this evening is 0mV between pipes and Earth - 160mV between pipes and Neutral - AC readings - mains on.The socket I'm using to test these voltages is at the immersion switch (circuit side not load side)- immersion circuit breaker off at the CU and off at the switch (immersion now completely disconnected and removed)- so this voltage must be coming via Neutral from the CU. Now, when switching OFF the upstairs lighting circuit, the pipes to Neutral falls immediately away to 10mV! Stays here for a while then after about 20mins builds back up to 160mV with the circuit still off!! Now we are losing hope!
;-[

Hope some of this makes sense.

Thanks to everyone - will be working on it again tomorrow - if you can be patient.

Tony H

[tonyh...@gmail.com]

Hi Onetap - interested to hear your views on the sacrificial anode - having been told on Friday by Ariston "Tech" that "...they don't use them anymore" - was talking to another "Tech" this morning about another poss solution and he said that they certainly do still have the anode - on the immersion - to protect the immersion! So, I said, if it's only there for that, without the immersion (which is currently on the floor in the airing cupboard - the anode won't be missed either? (Have blanked off hole with BRASS plug!!) What about the copper thermostat tube - that corroded and started to leak in the first place, when the last anode disintegrated? I asked. No answer to that!

What do you think is going to happen next without the anode in,Onetap? Thermostat tube bursts again? - SS cylinder develops leak ? Copper pipework in rest of house starts to corrode and leak?

Devil and the deep blue, here. Put immersion + anode in - lasts maybe 2 months, needs new immersion+anode.(£40) Don't replace it - themostat tube corrodes maybe 6months - replace (£80). Aaahhhh!

[tonyh...@gmail.com]

Hi Harry - SS immersion is only partially SS - they make the point that parts actually are copper and should be protected accordingly. Back to anodes again.

Thermostat tube - thought maybe titanium - £120 for 100mm - then need to find someone who can make it - weld/?? and provide the tapered screw thread to attach it to the cylinder.

Then I thought - nah!! ;-}

[tonyh...@gmail.com]

Thanks Andy - have been measuring everything in AC - on the assumption that any "breakdown in insulation" or earth leakage situation would be from an AC source. Take you point about the PD across EDF's PDE and my Ground Earth being best test as DC - obvious really but I didn't think of it. Anyway - they've said their reading s are within limits so I must look elsewhere.

One thought I'd had was perhaps to attach my Ground Earth to the PDE earth at the Service Box - it might take the 200mV somewhere else!! As you can tell - we're grasping at straws!!

Checked the water co - they have reassured us our ph is again as required.

The meter probes (with 500 ohm resistor load in parallel) have been placed at various times across house earth/neutral/pde earth/ground earth with main power on/off, MCBs and RCDs individually on/off at CU/SB on multiple occasions.

No, no DC generators nearby - live up farm track, 15 other properties - 3phase overhead distribution....nearest trains, diesels!

Anyway,grateful to have you guys to talk to, at least you understand what our problem is - Ariston/EDF/Plumber/Electrician - "..oh no, mate - never had this before.."!!

There's got to be an answer..... ;-}

[Andy Wade]

On 07/11/2011 15:51, Onetap wrote:

>> Yes, so... (current due to internal electrochemical effects, wot I said).
>
> Why say it and confuse the issue?

It was an attempt to clarify the issue. You seem to...

> Faraday says A unless B, but B applies, so we can ignore A and
> Faraday.
>
> 200mV is loads of PD to create a corrosion issue. I'm fairly sure that
> you couldn't produce that sort of voltage with mains water in a
> corrosion cell.

...have missed the point though. The 200 mV (AC) to an arbitrary earth
point is 'A' and won't cause the corrosion. Electrolytic effects that
do, 'B,' are independent of 'A'. There are probably a few million
cylinders that are a few volts AC above the local earth and that don't
have corrosion problems.

A more general question for the panel might be "how common are corrosion
problems in unvented cylinders?"

--
Andy

[Andy Wade]

On 07/11/2011 20:56, tonyh...@gmail.com wrote:

> One thought I'd had was perhaps to attach my Ground Earth to the PDE
> earth at the Service Box - it might take the 200mV somewhere else!!
> As you can tell - we're grasping at straws!!

Chasing red herrings, more like.

> There's got to be an answer..... ;-}

Some fault in the construction of the cylinder?

You could try
http://www.waterheating.fsnet.co.uk/wmadefault.htm
to see if they have a corrosion expert prepared to help.

--
Andy

[tonyh...@gmail.com]

Hi Andy have emailed www.waterheating.fsnet - will see if they reply. Needless to say, Ariston don't seem to be one of their contributors.

Has anyone here any experience of Ariston in terms of quality, service etc.?

Has anyone any experience of systems like these - www.heatweb.com - they don't seem to use stainless steel so in theory if mine is a "electrolytic" problem - being all copper might help. And I could put it in myself - agreed expensive but not as expensive as re-piping the whole house!!

Anyone want to buy a nearly new stainlees steel unvented 210lit Ariston HW cylinder - going cheap!! ;-{

Tony H

[Tim Lamb]

In message <9hr6at...@mid.individual.net>, Andy Wade
<spamb...@maxwell.myzen.co.uk> writes

I run our under sink hot water from the soft water side of the house
supply.

Could this be an issue here?

regards
>

--
Tim Lamb

[Dave Plowman (News)]

You'll always get a voltage reading between two points in one leg of a
circuit which is carrying current. That's how an ammeter works - it
measures the voltage drop across a very low resistance. So low it doesn't
effect the operation of that circuit.

--
*Most people have more than the average number of legs*

Dave Plowman da...@davenoise.co.uk London SW
To e-mail, change noise into sound.

[tonyh...@gmail.com]

Thanks Tim - but our water's classified on the soft side - we don't have a softener.

[tonyh...@gmail.com]

So Dave - can you help me with how to measure what I think is voltage in the pipes around the cylinder - one probe on the pipe, presumably and, without stating the obvious(!), what should I do with the other?

By getting an accurate and consistant reading of PD at the pipes, if there is one, then, by a process of elimination, I should be able to isolate the circuit that might be causing it - if you see what I mean?

If I can prove NO voltage - then no "galvanic corrosion" - problem not electrical, then. But I still think I have either earth leakage or stray voltage - either way it's making us very nervous about when it will corrode through again and leak next - and it's becoming a financial worry, too.

Anyway, thanks for your input.

[Dave Plowman (News)]

In article
<9705745.1050.1320762616188.JavaMail.geo-discussion-forums@yqjc16>,

No. Pipework could have additional earths near anywhere. Where say a
copper clip is attached to a wall. Or a metal sink. Or the boiler. Enough
to allow a small voltage to flow.

--
*The longest recorded flightof a chicken is thirteen seconds *

[John Rumm]

On 08/11/2011 14:32, tonyh...@gmail.com wrote:
> Thanks Tim - but our water's classified on the soft side - we don't have a softener.

Soft water can be more "aggressive" on plumbing metalwork in general.
Hard water tends to form an insulating layer of scale on all the water
contact surfaces of the pipework etc.



--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

[John Rumm]

Would one not need a DC flow in order to achieve any meaningful
electrolytic erosion and deposition of metal?

IIUC, galvanic effects usually occur independently of any external AC
mains influences.

[John Rumm]

On 08/11/2011 08:15, tonyh...@gmail.com wrote:

> Has anyone any experience of systems like these - www.heatweb.com - they don't seem to use stainless steel so in theory if mine is a "electrolytic" problem - being all copper might help. And I could put it in myself - agreed expensive but not as expensive as re-piping the whole house!!

I have spoken to them in the past. They seemed very helpful, so it might
well be worth giving them a call.

> Anyone want to buy a nearly new stainlees steel unvented 210lit Ariston HW cylinder - going cheap!! ;-{

Have you considered introducing some electrical separation between the
cylinder and everything else, if you are convinced this is an
electrically influenced problem? One could introduce sections of plastic
pipe in strategic places to leave the cylinder "floating" (especially if
the immersion is not connected)

[tonyh...@gmail.com]

Hi John - something you wrote there started me thinking - if it's AC voltage in the copper pipe - perhaps from inductance from an AC cable run somewhere in the house - or even some sort of "earth leakage" - surely it will only be AC going into the tank.

If you know, or I can prove, that AC current/voltage cannot cause "galvanic", or any other sort, erosion/corrosion then the problem is NOT the voltage in the pipes.

There's nowhere a DC voltage can be generated in the house. (Oh, just thought - could the "backup batteries" on the smoke detectors/electronic time switches etc. be feeding back into the system somehow - they'd be DC?

Any thoughts? Anyone?

Who knows we might be getting somewhere, fingers crossed that someone out there has the answer - DC only creates corrosion/erosion - not AC

Thanks all

[cynic]

AC is normally accepted as not causing galvanic corrosion as any ions
setting off from a pole (electrode) under one half cycle are returned
to whence they came during the second half cycle.
DC voltage will result from the presence of dissimilar metals iin a
system, set far enough apart in the periodic table whereby in the
presence of an electrolyte a simple cell is created and a current
flows.

[Dave Plowman (News)]

In article
<27607616.904.1320847241042.JavaMail.geo-discussion-forums@yqcm23>,

My view is you're taking a red herring up a blind alley...

--
*Why don't sheep shrink when it rains?

[tonyh...@gmail.com]

Thanks cynic, just what we hoped to hear. AC doesn't cause galvanic corrosion.

We understand that "... DC voltage will result from the presence of dissimilar metals in a system, set far enough apart in the periodic table whereby in the presence of an electrolyte a simple cell is created and a current flows.." Car battery etc...

However, do you happen to know what occurs between the "..dissimilar metals and electrolyte.." over a period of time when the current/voltage flows the opposite way - ie into them from external source - not generated by them? Hope that makes sense.

Now if I can prove it is AC in the pipes - it's got to be back to Ariston (the metal suppliers!)or the water company (the electrolyte providers). Can't think of anything else. Thanks again.

[tonyh...@gmail.com]

...>My view is you're taking a red herring up a blind alley..>

Hi Dave - you're not "cynic" by any chance,are you? Sorry if we're boring you ;-}

Just trying to resolve this thing quickly before leaks start appearing elsewhere in the house.

Were even talking to Megaflow yesterday who have reassured us that for £1800 we could change the cylinder for one of theirs and the short/medium-term corrosion problem would disappear!! All SS and Somethingalloy apparently. In fairness to them the guy we were talking to was seriously knowledgeable and helpful and concerned at our plight. We said we'd be back to him - just after the lottery win.

Anyway don't give up, Dave, you've been very helpful so far.

Thanks

[tonyh...@gmail.com]

>..A more general question for the panel might be "how common are corrosion
problems in unvented cylinders?" ..>

Good point, Andy - talking to a company of "Corrosion Experts" today and the guy there was asking me questions - why? It seems his mother had just forked out £800 on 2 plumbers to come and sort out corrosion problems with the immersion element anode on her ARISTON Unvented system! Coincidence? I think not!

[John Rumm]

On 09/11/2011 14:00, tonyh...@gmail.com wrote:

> Hi John - something you wrote there started me thinking - if it's AC
> voltage in the copper pipe - perhaps from inductance from an AC cable run
> somewhere in the house - or even some sort of "earth leakage" - surely it
> will only be AC going into the tank.

Indeed.

> If you know, or I can prove, that AC current/voltage cannot cause
> "galvanic", or any other sort, erosion/corrosion then the problem is NOT
> the voltage in the pipes.

Well I don't claim to be an expert on electrolysis, but my understanding
is that you would need a direct current flow to allow continuous
migration of ions from one electrode to another. Otherwise they will
migrate one way for half a cycle, then back again 1/50th of a second later.

> There's nowhere a DC voltage can be generated in the house. (Oh, just
> thought - could the "backup batteries" on the smoke detectors/electronic
> time switches etc. be feeding back into the system somehow - they'd be DC?

Galvanic corrosion will normally result when you have two dissimilar
metal electrodes in an electrolyte, that are also connected to each
other electrically. It needs no external power source since the setup
acts as a simple electrical cell and generates it own PD.

One can accelerate the process by driving a direct current through the
electrolyte. You can stop it by interrupting the circuit with the
interposition of an insulator.

[John Rumm]

On 09/11/2011 15:42, tonyh...@gmail.com wrote:

> We understand that "... DC voltage will result from the presence of
> dissimilar metals in a system, set far enough apart in the periodic table
> whereby in the presence of an electrolyte a simple cell is created and a
> current flows.." Car battery etc...
>
> However, do you happen to know what occurs between the "..dissimilar
> metals and electrolyte.." over a period of time when the current/voltage
> flows the opposite way - ie into them from external source - not generated
> by them? Hope that makes sense.

Current flow is current flow - regardless where the PD that causes it
comes from (i.e. internally generated, or externally applied). The
direction of current flow will dictate which way the ions migrate. Hence
the ability to charge a battery by driving current through it against
its normal direction.

[cynic]

On Nov 9, 3:42 pm, tonyhol...@gmail.com wrote:
> Thanks cynic, just what we hoped to hear. AC doesn't cause galvanic corrosion.
>
> We understand that "... DC voltage will result from the presence of dissimilar metals in a system, set far enough apart in the periodic table whereby in the presence of an electrolyte a simple cell is created and a current flows.."  Car battery etc...
>
> However, do you happen to know what occurs between the "..dissimilar metals and electrolyte.." over a period of time when the current/voltage flows the opposite way - ie into them from external source - not generated by them? Hope that makes sense.

Generally metal leaves from the Anode if that helps - hence
Sacrificial Anodes are used

>
> Now if I can prove it is AC in the pipes - it's got to be back to Ariston (the metal suppliers!)or the water company (the electrolyte providers). Can't think of anything else. Thanks again.

Most of the industrial cylinders and quite a lot of the domestic ones
are supplied with a sacrificial anode inside. The whole idea being
that this suffers the galvanic corrosion rather than the water
containing shell/pipes. Of course this does require a modicum of
maintenance in that it needs periodically checking and replacing as
required. Many of the domestics are welded in and not changeable but
will corrode away before the cylinder corrosion starts thus giving a
"design life extension" (just not too much or repeat sales suffer).
Without making too direct or libellous an attack you need to ask
around for similar stories as yours with the same manufacturer.