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Discuss Gledhill light unvented cylinder imploded in the Plumbing Jobs | The Job-board area at PlumbersForums.net

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Hi everyone,

Hope someone can shed light on this problem.
I’ve been and changed bath taps For a client by first isolating the cold mains.
I then opened the kitchen mixer tap to drain both hot and cold water and while that was draining, I went into the bathroom and opened the separate hot and cold bath taps.
The water started to slow down but the hot took a little longer to stop (no more then 1-2mins).
So I proceeded to remove the bath taps then suddenly the hot water started running from the pipe. At this stage the tap was already removed so I had to place my finger over the pipe to stop the water.
I asked the client to open the taps downstairs to which he replied “they are already open”
He then went into the loft to isolate the hot water outlet from the cylinder via a gate valve he had installed by the installer of the cylinder.
After replacing the taps, I asked the water to be switched back on and all looked well till the clients son shouts out that the boiler is leaking.
I went up into the loft and saw that the cylinder was leaking from the heating outlet into a polythene sheet made up into a box.
I isolated the cold mains and although the cylinder looked fine externally, the top had come away and the secondary outlet that was unused had moved away from its original position and poking out into the insulation of the cylinder away from where it should be. It was obvious that the cylinder had imploded and went near back into shape once the water was put back on.
At this point the client says to me “not again”
He then explained that that’s the second cylinder that’s imploded the first one five years ago and now this one. Apparently the first one imploded after the client changed a washer in one of the taps.
The cylinder is installed in the loft and it’s a detached 4 bedroom property with 2 bathrooms.

On inspection, the only thing I noticed is that the expansion vessel is installed on the hot water outlet instead of being installed after the combination valve on the cold inlet as illustrated on the manual
Would this void the warranty and cause such problem?

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The cold water supply to cylinder from the multifunction valve is coming off the wrong port.
 
Hi,
Neither am I gas safe no am I G3 qualified
I’m a competent plumber and install bathrooms for a living.
I’m not installing or touching the cylinder. I’m trying to get myself out of the liability and also to help my client resolve this issue.
 
The cold water supply to cylinder from the multifunction valve is coming off the wrong port.


Hi,
I had also noticed that.
Looking at the manual, it’s not in the right orientation.
The main thing I noticed was the expansion vessel.
They may be other problems but as I’m not G3 qualified, I can’t comment on the installation.
I just want to arm myself with as much information for the client to either get a replacement cylinder or get the installer to take liability.
 
Then first things first get a G3 qualified engineer in to assess the situation. My guess is that no one checked the install was correct on first or second install so I’d say you’re ok
 
First things first are you G3 qualified?

Hi,
I’ve just been searching for G3 qualification.
First thing that came up on the search was Gledhill g3 corse. 1 day £90 to become G3 qualified??
I would do the course just to have that qualification.
 
If you can persuade the Client, I would get Gledhill out to view and comment on the installation / collapsed tank.

Whilst you don’t need to be G3 qualified to change washers et al on a pressurised system, you really do need to understand the principles of how the system operates and the importance of venting when draining it down.

Often these things are not clear cut.

Personally, I don’t think that the G3 course covers sufficient detail about the process and need to avoid the creation if a vacuum in an unvented cylinder. It is very easy to do this unintentionally when draining down an unvented system when the tank is at or near the highest point of the installation. Draining off bellow the tank with the cold water supply isolated has the potential to create a vaccum in the vessel. I suspect this is part of the problem here - or did you ensure that the tank could freely vent either from the prv or preferably by slackening the hot water draw off connection.

Think of the tank like a crisp packet - it takes a hard blow to burst it, but only a very gentle suck to collapse it.
 
Incorrect installation, tell customer to contact the manufacturer for their take on it.

100% agree. However! This needs to be done by the customer. The reason for that is if you do it then you become kind of 'tainted' by association and the customer needs to understand you are stood alongside them rather than doing it for them - hope that makes sense?

Def def def get them in. Once that's done then the customer can call the last installer back to correct it. Even if the last installer simply replicated what was there, they still have a duty of care to do the job properly. Obviously, if they were not G3 then that's yet another issue.

My advice? Stay 'close', help, but not too much.

Let us know how you get on.

PS. The course is well worth doing, BUT prepare to spend the rest of your life learning what's NOT taught ;)
 
Reality Rakesh,
Dislike me for all you want. I've had a few!!!

You're the last person on the job, and your work caused the cylinder to implode.
Get a report from the Manufacturer and so on, the customer will be without hot water for weeks while you wait for a resolution.

I feel the customer is not going to back you up, when waiting weeks for an insurance provided hot water system replacement.

The customer will want hot water and you're the bloke they are going to pursue to get it.

As said, I hope you have insurance

Have a nice day!!!!!!
 
Yes, Dave, you are correct in the process to follow.

The reason I referred to Gledhill, or indeed any accredited independent was, that I think that the guy who replaced the washers is at risk of being blamed for the failure.

I regard high level (particularly attic) unvented installations as being “riskier” than the norm when they are not in their operational state.

If the cold water inlet to the tank is incorrectly installed and not being fed through some form of non return valve ( I cannot see from the picture how the tank is fed). When draining the cold water system, if all the hot taps are turned off and if you isolate the cold water at the house stopcock and open the cold kitchen tap, you will pull a vacuum in the tank equivalent to around a 3m head of water (assuming the tank is in the attic if a two storey house). That will be released once it can be balanced by a freely venting hot water tap ( ie no nrv). However, the hot water tap, when opened will also pull a vacuum, that will be released once it can be overcome by the cold water “pull”. If the hot tap has an nrv on it, then the position then the pull will continue to increase. This is probably why when he thought the system was empty, the hot water suddenly flowed. At that point the vacuum had almost certainly bbbeen broken by the tank collapsing.

This is quite important, because without this evidence, the initial conclusion could be that the system was drained incorrectly.
 
If you can persuade the Client, I would get Gledhill out to view and comment on the installation / collapsed tank.

Whilst you don’t need to be G3 qualified to change washers et al on a pressurised system, you really do need to understand the principles of how the system operates and the importance of venting when draining it down.

Often these things are not clear cut.

Personally, I don’t think that the G3 course covers sufficient detail about the process and need to avoid the creation if a vacuum in an unvented cylinder. It is very easy to do this unintentionally when draining down an unvented system when the tank is at or near the highest point of the installation. Draining off bellow the tank with the cold water supply isolated has the potential to create a vaccum in the vessel. I suspect this is part of the problem here - or did you ensure that the tank could freely vent either from the prv or preferably by slackening the hot water draw off connection.

Think of the tank like a crisp packet - it takes a hard blow to burst it, but only a very gentle suck to collapse it.


Hi,
Thanks for the reply.
The first thing I did was to read the manual on draining down the system. Yes as you mentioned, negative pressure created in a cylinder can cause it to Implode, however on a call I made to Heatrea sadia technical support, I’d gone through the exact step by step process of drain down, changing taps and filling back up.
The technical guy responded by saying that there was no way of imploding the cylinder with the steps I’d taken.
The cylinder would need 15 bar of negative pressure to explode or implode.
Now as you’ve mentioned, I looked up on drain down of said cylinder and sure enough there is a drain down procedure.
No, I did not drain down as per instructions, so yes, working on any of the plumbing involving the drain down of the cylinder is my responsibility and liability.
Anyone who works on any dwelling is liable regardless. There should be a proper understanding of any system installation to work on it safely.
Now I have been on this forum for some time and admittedly use it to learn of other people’s experiences.
Knowledge and experience is key, so i would like to think that I don’t undertake any work without prior knowledge.
In this instance, I admit to not knowing or researching proper drain down procedure of the installation so the only way is for me to understand what I have done or what has caused the cylinder to implode. Not only this one but also the previous one.

I’ve been installing bathrooms for the last 15 years and am proud of every single installation without any major failings. Yes the odd leak in joints and fittings but not a major failure like this.
Every day we learn something new or old but I learn something every day and never have I claimed to know everything.

Anyway, back to why you’ve rightfully mentioned....... correct drain down procedure!
I’ve taken an image of the manual and have also discussed this with couple of heating engineers, one of which I know who’s installed this cylinder.
They both admit to not knowing this drain down procedure.

All I’m doing is waiting for Gledhill to get back to the plumbing merchant I use and document everything for the client to take up with the installer.

Thant you all for your input and sharing your knowledge to point out the possible faults.
I really appreciate the input

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Reality Rakesh,
Dislike me for all you want. I've had a few!!!

You're the last person on the job, and your work caused the cylinder to implode.
Get a report from the Manufacturer and so on, the customer will be without hot water for weeks while you wait for a resolution.

I feel the customer is not going to back you up, when waiting weeks for an insurance provided hot water system replacement.

The customer will want hot water and you're the bloke they are going to pursue to get it.

As said, I hope you have insurance

Have a nice day!!!!!!


Hi Oz,
I don’t deny any wrong doing.
Fortunately, I have discussed all my findings with the help of this forum and have advised the client of the possibility that the cylinder is incorrectly installed.
I’ve also shown him the paragraph relating to drain down procedure to show that while I didn’t carry out the procedure, I have called technical support of a different manufacturer to find if what I have done by changing the taps and draining down exactly as I did would cause the cylinder to implode.
As Mentioned, it would take 15bar of negative pressure to implode a tank so I am doing everything to come to a resolution.
If I have to pay for a new tank and install it then I will do it.
The client is being understanding and thanked me for investigating the matter.
He has been let down by two installers first one of which incorrectly installed it and second installer just changed the tank for an identical one without changing or checking that it was correctly installed in the first place.
The installer has also been serving the cylinder since the install so if what’s been mentioned here is correct then the installer has no clue on what he’s doing.
I would say if the installation is incorrect then the liability lies with the installer.
If I’m proved to be in the wrong then I will correct it.
 
I would have opened the hot draw off connection on cylinder once supply water was off, before I would have opened lower taps.
Had to replace a leaking combination valve on a first floor unvented unit (valve installed wrongly at low level) and I opened the nut to top of cylinder on hot outlet.
Customer was surprised I did that, but I showed him the strong suction created by putting my hand on outlet and releasing it
 
Hi Oz,
I don’t deny any wrong doing.
Fortunately, I have discussed all my findings with the help of this forum and have advised the client of the possibility that the cylinder is incorrectly installed.
I’ve also shown him the paragraph relating to drain down procedure to show that while I didn’t carry out the procedure, I have called technical support of a different manufacturer to find if what I have done by changing the taps and draining down exactly as I did would cause the cylinder to implode.
As Mentioned, it would take 15bar of negative pressure to implode a tank so I am doing everything to come to a resolution.
If I have to pay for a new tank and install it then I will do it.
The client is being understanding and thanked me for investigating the matter.
He has been let down by two installers first one of which incorrectly installed it and second installer just changed the tank for an identical one without changing or checking that it was correctly installed in the first place.
The installer has also been serving the cylinder since the install so if what’s been mentioned here is correct then the installer has no clue on what he’s doing.
I would say if the installation is incorrect then the liability lies with the installer.
If I’m proved to be in the wrong then I will correct it.

Rakesh.
Taken to a court of law, although I cannot obvs guarantee it, I am certain the main liability would sit with those who installed and subsequently serviced this installation.

Many people think once the 12 month warranty is up they can walk away scott free. That is UTTERLY WRONG. As a professional, especially charging for a service, you have an ongoing liability for the installation.

On a seperate note, I take my hat off to you. To publically say you would take responsibility says a lot about you. You seem one of life's good guys so I, at least, will try to support you going forward.

Please keep us abreast of what happens.
 
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Hi All,
Just a follow up and attached previous rejection letter for a warranty claim on the first cylinder.

Having spoken to Technical, they need the cylinder sent back to them for inspection.
They obviously don’t check the installation but just assess the cylinder for manufacturers defects as informed by the technical department.
They straight away mentioned page 22 of the manual for drain down procedure and also page 16 for the importance of the drain down procedure.
Now I’ve always wondered how an implosion would occur on an unvented cylinder. Well, now I know.
So it sounds like the negative gravitational force from both the hot draw off and cold inlet may have caused the cylinder to implode.
With the fact that the combination valve may be incorrectly installed, the check valve may have been bypassed. I don’t know this for sure but will have to get a qualified G3 installer to give a full report.
I also don’t know if the expansion vessel being installed to the hot water draw off has had a any detrimental effect.
So even if the cylinder is incorrectly installed, I may still be liable for not knowing how to drain down the cylinder to carry out any plumbing work

When I asked Gledhill technical how much pressure both negative or positive required to damage the cylinder, they were unable to comment. I also mentioned that I’d called Heatrae Sadia and went through the same scenario, however I was told by their technical team that there is no way their cylinder would implode under those circumstances and that there would have to be 15 bar of negative pressure to explode or implode their cylinders.
Again he pointed out the two paragraphs on their manual referring drain down procedure of their cylinders and could not comment on other manufacturers.

Could anyone refer a G3 qualified experienced engineer to give me a report on the installation in the Nottingham area?

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All Gledhill stuff is absolutely rubbish, I have never come accross such badly designed equipment ever. The company now makes more money from fixing and service contracts repairing their rubbish stuff than they ever made from selling them, the main company went bust. You only have to see the cohorts of service vehicles headed up and down the motorway from Blackpool everyday where these appauling products where designed and cobbled together on Friday afternoons after they had been to the pub...centralheatking
 
The expansion vessel on the hot would still take up expansion.
The combination valve is wrong but I can’t see how this would cause the cylinder to implode
 
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The expansion vessel in the hit would still take up expansion.
The combination valve is wrong but I can’t see how this would cause the cylinder to implode

It must be something to do with the Non Return valve in the combination valve. Maybe as the cylinder can drain backwards through the cold feed, and drain through the hot side causing Negative pressure?
 
That all sounds like typical manufacturer b.s, in order to get out of replacing the cylinder. To simply say that it's not our fault without offering an explanation is laughable!
Worcester specifically state that an anti vacuum valve is required if the top of the cylinder is 15m or higher. I was told that the reason for this is that they use sectional insulation instead of a bonded insulation. The bonded insulation strengthens the cylinder and makes it less likely to implode.
It sounds as though you have been competent in your work. The cylinder has not been fitted correctly and this is the most likely cause of the fault.
Good look with this one.
 
Fitted a Viessmann cylinder a couple of months ago which I believe is made by Gledhill and it was supplied with a small 1/2” valve that will allow air into the cylinder if there’s a negative pressure, like an automatic air vent in reverse. There was no mention of it in the instructions but it was obvious what it was for. Personally I think these cylinders are rubbish, they seem too flimsy, the connections can wobble around quite a lot.
 
is hazard a guess that bypassing the check valve has allowed it to siphon out.... probably through the hot draw off, that’s why Rakesh says water started coming out of the hot pipe. As we all know, you only need a litre or so to start a siphon off

Just an idea like
 
Rakesh

For an accepted analysis of the failure will need a report prepared under Pressure Systems Safety Regulations (PSSR). The G3 qualification is to demonstrate competence to instal and commission. Whilst that would possibly help you, I think you would be better with a fault tree analysis report that covers both design and installation and thereafter, the operating situation that probably caused the failure.

As an aside, I don’t think that the information given to you by Heatrae Saudia (spelling ?) is correct. To resist a vacuum of delta 15bar against atmospheric pressure, the wall thickness of a 315 stainless 200 litre tank would need to over 10mm thick.

Andrew
 
When I asked Gledhill technical how much pressure both negative or positive required to damage the cylinder, they were unable to comment. I also mentioned that I’d called Heatrae Sadia and went through the same scenario, however I was told by their technical team that there is no way their cylinder would implode under those circumstances and that there would have to be 15 bar of negative pressure to explode or implode their cylinders.

The Heatrae Sadia advice is either misquoted or wrong. The tank would need to be built like a submarine to withstand a pressure of 15 bar before collapsing. It would also need to be evacuated and then immersed in water to a depth of 150 m to achieve a 15 bar pressure difference.

The Gledhill warning notice states that emptying the cylinder while hot, sealing it, and then letting it cool will cause damage. Assuming that the cylinder starts at atmospheric pressure and 60°C at the time it is sealed then cools to 20°C. From this, we can deduce that a pressure difference of 0.12 bar or less may be sufficient to cause damage due to collapse.
 
The drain down procedure is irrelevant. You didn't drain the cylinder.

Unless the cylinder syphoned down the cold because the combi valve was fitted wrong.

I would not expect something like this to happen when just cutting the flow to change a few taps.


I’m thinking the same thing. I do t know how it would siphon from the hot water draw off. I’m thinking back siphon from cold inlet as the hot can only draw off from the very top of the cylinder.
Unless my understanding of the internals of an unvented cylinder is completely wrong.
 

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