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IDC

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14
Hi all,

Looking for some advice as a previous posting suggested there are some people quite experienced with Gledhill system on the forum.

I'm having an issue whereby when the hot water has been on and any hot water tap/shower outlet is opened, the hot water pressure is significantly higher than usual. It then returns to normal after a few seconds. If however, the tap/shower is turned on full to the hot, there is a loud vibration and pipe rattling in the area where the cylinder is housed.

(Please upload the video directly to the post rather than linking elsewhere - the content will one day be erased and we are left with a broken post link then)

Once the pressure has returned to normal through opening a hot water outlet, this issue will not occur again until the hot water has been on again. The cold water pressure is totally unaffected and does not cause the vibration/high pressure when in use on any occasion.

There is no water dripping through the Tundish.

The PRV and expansion vessel have both been replaced earlier in the year and have been verified by the engineer as being installed correctly and the PRV is the correct rating.

The Geldhill engineer who visited today recommended that we change our expansion vessel to a 25 litre capacity, from the current 18. Having looked at the manual, it appears that the recommended size expansion vessel for this system is 18 litres. At the time, the engineer inferred that the vessel fitted was the incorrect size, however, the manual seems to suggest this is not the case.

I've had a number of different people (G3 certified) look at this issue and no one can pinpoint the source of the problem (hence why turning to Gledhill directly).

A previous engineer suggested that it is common to have to put the expansion vessel on its side to prevent/limit virbations/noises, however, due to area where the cylinder is housed, this isn't an option unfortunately.

Another has suggested cold water backfilling the system could be the issue, however, I would assume this would mean this vibration/noise would happen far more frequently.

Keen to see if any has experienced similar issues and can shed some light on whether the suggestion of a larger vessel is really going to help?

Obvious caveat, I'm not working on any of this myself!

Thanks
 
Last edited by a moderator:
Can you take a pic of the pipework and controls on the left hand side of the cylinder .

Yeah sure - I'll pop one up.

After seeking a bit more clarification from the engineer, it would appear that the system is not using a balanced cold feed. (Not too sure why, as this system was installed prior to me owning the house) and the suggestion of using a larger expansion vessel is to take up the extra expansion in the system caused by the balanced cold feed.

If the feed isn't balanced, would it be possible that what I'm experiencing is excess pressure caused by the unbalanced cold backfilling into the system? Presuming so, would a larger expansion vessel aid/solve this?
 
An unbalanced feed can potentially cause problems , but theres a few things to check first , however asuming the Gledhill guy is “ switched on “ I am pretty sure he would have seen any faulty pipework .
 
An unbalanced feed can potentially cause problems , but theres a few things to check first , however asuming the Gledhill guy is “ switched on “ I am pretty sure he would have seen any faulty pipework .

Here's a few pics

Expansion vessel - The nut coming off the hot water out the tank is because at some point, someone had attached the expansion vessel there (God knows why)

Screenshot 2019-09-26 at 10.14.03.png


Central heating filler loop coming off the mains.

Screenshot 2019-09-26 at 10.13.55.png


Inlet group (PRV and NRV) with expansion vessel coming off.

According to the manual "The cold water supply to any mixer taps/showers must be taken from the cold water tapping of this valve to ensure balanced hot and cold pressures. This valve is factory set to ensure the correct operating pressure for the Stainless Lite".

Screenshot 2019-09-26 at 10.40.55.png


I'm assuming this is where my problem is with regard to not having balanced cold?

Screenshot 2019-09-26 at 10.14.23.png


Tundish and PRV coming off tank

Screenshot 2019-09-26 at 10.13.45.png
 
blimey that lot isnf half sandwiched in there.
It doesnt help anybody trying to help , not your fault but can you take a pic slightly further back I / we need to see where the ex vessel is fed from , its hard to tell but does it go back to the tee under the inlet control set ( red valve )
 
blimey that lot isnf half sandwiched in there.
It doesnt help anybody trying to help , not your fault but can you take a pic slightly further back I / we need to see where the ex vessel is fed from , its hard to tell but does it go back to the tee under the inlet control set ( red valve )

Yeah, I don't think the previous owners/original installer thought about future maintenance!

The expansion vessel is indeed fed to the T under the inlet control valve. I've marked it below

Screenshot 2019-09-26 at 15.01.55.png


I am under the impression that it would ideally be attached to the inlet control valve, but it doen't look like there's enough space without having a super-tight bend in the pipe.
 
Yes its correct, personally I like them in the correct port on the ICS , but teed in there is fine .
Excessive cylinder temps wont help , is the cylinder stat set at 55/60 degrees?
What is the ex vessel pressure, did the engineer actually check it ?
Have you any idea on the incoming mains pressure is ?
 
Yes its correct, personally I like them in the correct port on the ICS , but teed in there is fine .
Excessive cylinder temps wont help , is the cylinder stat set at 55/60 degrees?
What is the ex vessel pressure, did the engineer actually check it ?
Have you any idea on the incoming mains pressure is ?

Cylinder temp is set around 50 . Had previously tried dropping the temp right down over the course of a few days to see if it made a difference, but it did not.

Not too sure on the incoming pressure as no pressure gauge anywhere in the system.

I don't believe the engineer checked the pressure in the expansion vessel, but, it was a new vessel less than 2 months ago. I guess I can just get a schrader-based pressure guage and attached it to the port to verify?
 
Possibly worth having having a pressure gauge fitted on your incoming mains and also on the tank inlet after the combination valve.

It may seem to be a bit of overkill, but it makes it so much easier to work out what is going on.

I assume that (in the absence of a balance cold) you have checked all/any mixer taps / valves for high pressure cold back feeding the system?
 
Possibly worth having having a pressure gauge fitted on your incoming mains and also on the tank inlet after the combination valve.

It may seem to be a bit of overkill, but it makes it so much easier to work out what is going on.

I assume that (in the absence of a balance cold) you have checked all/any mixer taps / valves for high pressure cold back feeding the system?

Ok sure, I'll look into getting that done. Hopefully space isnt at too much of a premium after the combination valve (as you can see from the above, it's pretty tight!)

What would be the best way to check for the cold feeding back? I assume turn off each tap/mixer over the course of a few days to try and see if turning one off stops the issue? If identified as the problem, is the fix to have a non-return valves fitted?
 
IDC,

Ideally work logically through the system to eliminate all the potential causes. The starting point is the incoming mains static pressure. If that is around 4 bar there is unlikely to be an issue for back feeding, but if it is above 6 bar - it could be an issue. Look at all the potential feed in points ( the kitchen mixer is often suspect No 1). Easiest way to test is isolating the mixer on the cold feed and see how the system performs or look for passing through the valves - but that can be difficult to spot sometimes. If that tap is an occasional source of water hammer that too can be an indicator it is passing. If a mixer is suspect I would replace it with a quality brand and not mess around with nrv’s. In my experience shower valves are the least likely suspect (but not always). Better still, if possible, convert to a balanced cold supply

A good G3 engineer who logically works through the system really should be able to solve this for you in a couple of hours. The problem is that some just jump to conclusions, then embark on the systematic replacement of all the the parts until it works or you run out of money!

I probably should not say this, but the G3 course / qualification is just one day ( training and exam). It focuses on the safe installation and operation of pressurised systems. Whilst the basic principles of the system are covered, very little, if any, training is given on fault finding or optimising the operation of the system.

Final points, never assume that the problem is just one issue and don’t tinker with the installation after the combination valve.

Hope this helps
 
IDC,

Ideally work logically through the system to eliminate all the potential causes. The starting point is the incoming mains static pressure. If that is around 4 bar there is unlikely to be an issue for back feeding, but if it is above 6 bar - it could be an issue. Look at all the potential feed in points ( the kitchen mixer is often suspect No 1). Easiest way to test is isolating the mixer on the cold feed and see how the system performs or look for passing through the valves - but that can be difficult to spot sometimes. If that tap is an occasional source of water hammer that too can be an indicator it is passing. If a mixer is suspect I would replace it with a quality brand and not mess around with nrv’s. In my experience shower valves are the least likely suspect (but not always). Better still, if possible, convert to a balanced cold supply

A good G3 engineer who logically works through the system really should be able to solve this for you in a couple of hours. The problem is that some just jump to conclusions, then embark on the systematic replacement of all the the parts until it works or you run out of money!

I probably should not say this, but the G3 course / qualification is just one day ( training and exam). It focuses on the safe installation and operation of pressurised systems. Whilst the basic principles of the system are covered, very little, if any, training is given on fault finding or optimising the operation of the system.

Final points, never assume that the problem is just one issue and don’t tinker with the installation after the combination valve.

Hope this helps


Thanks for the advice. It has been very frustrating so far as, like you've alluded to, I've had expansion vessel and combination valve replace so far, and now suggestion of larger expansion vessel (all from different people), but no checks on if the expansion vessel is correctly pressured, or, as you say, if there is feedback from one of the outlets.

I don't suppose there is anyone here who covers Surrey area on this forum who might be able to offer a thorough troubleshooting/solution?
 
I don't believe the engineer checked the pressure in the expansion vessel, but, it was a new vessel less than 2 months ago. I guess I can just get a schrader-based pressure guage and attached it to the port to verify?
Someone else may have made the point already (sorry, haven't time to read the whole thread in detail right now) but I think it is worth emphasising.

To work correctly the expansion vessel has to contain the correct total amount (moles) of gas, usually air. One explanation for the symptoms the OP described is a pressure vessel that is undercharged. The manufacturer's instructions are a choreographed routine for getting the right amount of air in and need to be followed carefully. Just pumping/bleeding air in/out to achieve a target pressure without knowing the state of the system isn't enough because it doesn't tell you the total volume of air that ends up in the EV.
 
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Someone else may have made the point already (sorry, haven't time to read the whole thread in detail right now) but I think it is worth emphasising.

To work correctly the expansion vessel has to contain the correct total amount (moles) of gas, usually air. One explanation for the symptoms the OP described is a pressure vessel that is undercharged. The manufacturer's instructions are a choreographed routine for getting the right amount of air in and need to be followed carefully. Just pumping/bleeing air in/out to achieve a target pressure without knowing the state of the system isn't enough because it doesn't tell you the total volume of air that ends up in the EV.

Ok thanks, sounds like starting with the EV pressure is the best bet. What should I expect an engineer to do to ascertain what the pressure in the vessel should be?
 
What should I expect an engineer to do to ascertain what the pressure in the vessel should be?
They should consult (or know by heart) the instructions provided by the manufacturer. The procedure is typically to close the CW inlet, reduce the pressure in the DHW to 0bar (gauge), pre-charge the EV to whatever pressure is to be used for the DHW, say 3bar. Open the CW inlet and the DHW will come up to 3bar. This loads the maximum amount of gas into the EV, which will minimise the pressure rise when the water in the system expands due to heating. I say 'gas' rather than 'air' as nitrogen is sometimes used instead.

A competent plumber with a G3 ticket won't need any supervision to get this right and will happily explain what they are doing and why if you show a polite interest.
 
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You really need to know your water pressure .
Personally I wouldn't advise gauges , test point maybe .
As for the engineer who didnt check the vessel, I am lost for words , its the first thing to check . The fact it was only fitted 2 months ago makes no difference, was it set then ?
 
Before we go wild thinking of everything under the sun that could be at fault here, the symptoms the OP has described would indicate a debris-filled strainer in the group inlet, or a faulty pressure reducing cartridge in the GI.

Pretty much every system I have attended where the pressure/flow rate is blasting out the tap and dying down, it was a partially blocked strainer causing it. Blocked strainers + mains water pressure + pressurised cylinders with expansion vessels = Weird noises and performance issues.

That's the first place a G3 engineer (and G3 they must be!) should look when encountering this symptom. Then have a look at all the other things one would normally do on a service.
 
Before we go wild thinking of everything under the sun that could be at fault here, the symptoms the OP has described would indicate a debris-filled strainer in the group inlet.

Pretty much every system I have attended where the pressure/flow rate is blasting out the tap and dying down, it was a partially blocked strainer causing it.

That's the first place a G3 engineer (and G3 they must be!) should look when encountering this symptom. Then have a look at all the other things one would normally do on a service.


Thanks for the suggestion. The group inlet was only changed a couple of months ago, but will get that looked at.
 
Hi all,

Looking for some advice as a previous posting suggested there are some people quite experienced with Gledhill system on the forum.

I'm having an issue whereby when the hot water has been on and any hot water tap/shower outlet is opened, the hot water pressure is significantly higher than usual. It then returns to normal after a few seconds. If however, the tap/shower is turned on full to the hot, there is a loud vibration and pipe rattling in the area where the cylinder is housed.

(Please upload the video directly to the post rather than linking elsewhere - the content will one day be erased and we are left with a broken post link then)

Once the pressure has returned to normal through opening a hot water outlet, this issue will not occur again until the hot water has been on again. The cold water pressure is totally unaffected and does not cause the vibration/high pressure when in use on any occasion.

There is no water dripping through the Tundish.

The PRV and expansion vessel have both been replaced earlier in the year and have been verified by the engineer as being installed correctly and the PRV is the correct rating.

The Geldhill engineer who visited today recommended that we change our expansion vessel to a 25 litre capacity, from the current 18. Having looked at the manual, it appears that the recommended size expansion vessel for this system is 18 litres. At the time, the engineer inferred that the vessel fitted was the incorrect size, however, the manual seems to suggest this is not the case.

I've had a number of different people (G3 certified) look at this issue and no one can pinpoint the source of the problem (hence why turning to Gledhill directly).

A previous engineer suggested that it is common to have to put the expansion vessel on its side to prevent/limit virbations/noises, however, due to area where the cylinder is housed, this isn't an option unfortunately.

Another has suggested cold water backfilling the system could be the issue, however, I would assume this would mean this vibration/noise would happen far more frequently.

Keen to see if any has experienced similar issues and can shed some light on whether the suggestion of a larger vessel is really going to help?

Obvious caveat, I'm not working on any of this myself!

Thanks
I've moved this thread to the normal UK plumbing forum. And also removed the link to the video. Rather than doing that, in future just click the Add Video button in the post and add it directly to the forum. That saves us having a broken link come next month when you've cleared out your Google Drive clutter. :) :D
 
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