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Discuss Cold water flow problem has stumped 3 plumbers...can you help?! in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

A

Alexwales

Afternoon all - We have a problem with very little/no cold water flow on the ground and first floor of our (fairly new build, 7 years old) 3 story town house. All flow is fine on the top floor and the hot water is unaffected and runs throughout the house.

It's an unvented, balanced system.

The network of pipes and valves are on the top floor next to the hot water cylinder. In this area we've had 3 plumbers in who have between them:

1. Replaced the Pressure relief valve 2. All non-return valves and taps replaced. 3. Tried changing direction of one non-return valve. 4. Tried pumping hot water back into the cold. 5. We've also has the water board check the mains and it's all fine.

But unfortunately we still have the issue! If anyone has any ideas, suggestions, that would be HUGELY appreciated at this stage. Thanks
 

Chuck

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Is this a new problem, or has it always been like this?
If new, did it start suddenly or get progressively worse over a period of time?
Is the pipework copper or plastic?
 

John.g

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2,832
Is the balanced cold just supplying the top floor?, may have a separate PRV supplying the bottom floor, shouldn't be that hard to determine.
 
A

Alexwales

Is this a new problem, or has it always been like this?
If new, did it start suddenly or get progressively worse over a period of time?
Is the pipework copper or plastic?

We've been in the house from new, 7 years. It's never been an issue before. Just stopped one day.

Pipework (at least all visible pipework) is copper.
 
A

Alexwales

Is the balanced cold just supplying the top floor?, may have a separate PRV supplying the bottom floor, shouldn't be that hard to determine.

Our understanding is it's all on the same system as there are no other visible pipes or PRV other than what is in the top floor airing cupboard with the hot water cylinder.

I will try and post a photo if possible.
 

Alexwales

Messages
21
Is this a new problem, or has it always been like this?
If new, did it start suddenly or get progressively worse over a period of time?
Is the pipework copper or plastic?
A new problem - we've been in the house since new, 7 years, and it happened virtually overnight.

All visible pipework is copper.

Cheers
 

Alexwales

Messages
21
Is the balanced cold just supplying the top floor?, may have a separate PRV supplying the bottom floor, shouldn't be that hard to determine.
Our understanding is the balanced cold supplies the whole house, as there is only 1 visible PRV. I'll attach photos if that helps, all taken from top floor airing cupboard.

The mains is second from left, where we've replaced the PRV. The cold is then good on the top floor and to the hot water cylinder, but is not going back downstairs.

4th pipe along from left we've replaced the tap and non return valve and still no flow.
 

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ShaunCorbs

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What is the 5th pipe from the left with a NRV? on it?
Where is the expansion vessel teed off?.

Balanced cold

Expansion vessel is inside the cylinder aka megaflow
 

John.g

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2,832
Finding it a bit confusing........working backwards from the cyl cold feed, would expect ERV, NRV then balanced cold (then PRV)., so this is the same in practice??. with NRV on balanced cold opening downwards??
 

Devisham

Authorising Engineer (Water)
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Should be a single check valve on the incoming MCWS feed to the cylinder to prevent possible HWS backflow only. Not sure why you have another single and a double check on the other bit pipework there, will be a flow restriction. I would also relocate the PRV closer to the inlet pipe feeding in to the cylinder only as you are restricting the whole system in its current position.
 
Last edited:

Gasmk1

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Is it possible that the incoming mains is split with one feeding the cylinder the other section feeding the other outlets, with a pressure reducing valve on that part of supply
 

John.g

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From post #7 "4th pipe along from left we've replaced the tap and non return valve and still no flow." this is the problem flow , there seems to be a NRV after the lever valve and other fittings further down, maybe another double NRV? don't know what their purpose is.
 

ShaunCorbs

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From post #7 "4th pipe along from left we've replaced the tap and non return valve and still no flow." this is the problem flow , there seems to be a NRV after the lever valve and other fittings further down, maybe another double NRV? don't know what their purpose is.

Repair coupling eg slip
 

Ben-gee

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I would remove the non-return valves and replace with plain pipe, in a systematic fashion until problem is resolved. Then add back in the necessary ones - using new ones.
If problem persists even with no nrv , then need to look elsewhere in system. In this case I would leave all as plain pipe until problem found.
Obviously would not leave property until the nrv were back in place.
 

Alexwales

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21
Thanks for all the replies - all helpful. I have a new pair of eyes coming in today - I will pass on the suggestions to him and report back, we'll look for another NRV or PRV, although if there is one, it's hidden under the floor boards or in the wall...😫

I did look under the kitchen cabinet today and the pipes are plastic when heading under the floor boards, if that makes any difference.
 

scott_d

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Non return valves on the wrong way round?
Arrows should Point down?
 

Chuck

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I did look under the kitchen cabinet today and the pipes are plastic when heading under the floor boards, if that makes any difference.
Plastic pipe can kink or collapse if, for example, its path includes a bend sharper than the manufacturer's minimum spec. Normally manifests much sooner than seven years after installation but if 'three plumbers' have not been successful at finding the problem that makes something out of the ordinary much more likely.

You are reaching the point where you need to adopt a properly systematic approch, i.e. a boroscope and some patience to construct a diagram of the pipework and then start a 'divide and conquer' process to pin down the location of the problem.
 

Last Plumber

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When you said the water board came and tested and all's well. What pressure did they say you had?
How high is the airing cupboard from ground?
I presume they tested and told you the pressure at ground level?
 

John.g

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2,832
When you said the water board came and tested and all's well. What pressure did they say you had?
How high is the airing cupboard from ground?
I presume they tested and told you the pressure at ground level?
The ground floor has the poorest pressure and as all the balanced colds are from one PRV at airing cupboard level then the ground floor flow should be slightly > the others due to its negative elevation, this is the mystery?.
 

Alexwales

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21
When you said the water board came and tested and all's well. What pressure did they say you had?
How high is the airing cupboard from ground?
I presume they tested and told you the pressure at ground level?
My wife was home when the waterboard came so I didn't get all that info i'm afraid - however - as the water pressure to the cylinder and top floor shower/taps have remained unchanged, the plumbers who've been in already feel that the water pressure is good, certainly not poor enough to be good flow upstairs and a tiny trickle downstairs! Cheers
 

Alexwales

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The ground floor has the poorest pressure and as all the balanced colds are from one PRV at airing cupboard level then the ground floor flow should be slightly > the others due to its negative elevation, this is the mystery?.
From reading all your replies and the fact that the previous plumbers were all stumped by it - it seems that it's increasingly pointing towards some kind of blockage further down the system - either a massive airlock, foreign debris or a failed valve/pipework which has been hidden behind a wall or under a floor after installation. It's the latter i'm most worried about as that will no doubt involve expensive exploration....
 

Last Plumber

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The ground floor has the poorest pressure and as all the balanced colds are from one PRV at airing cupboard level then the ground floor flow should be slightly > the others due to its negative elevation, this is the mystery?.
The ground floor has the poorest pressure and as all the balanced colds are from one PRV at airing cupboard level then the ground floor flow should be slightly > the others due to its negative elevation, this is the mystery?.

The ground floor has the poorest pressure and as all the balanced colds are from one PRV at airing cupboard level then the ground floor flow should be slightly > the others due to its negative elevation, this is the mystery?.
Are the cold draw offs on ground direct from mains or from that balanced supply on the top floor?

If they are direct, then my thoughts on the cause are wrong.
 

Last Plumber

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My wife was home when the waterboard came so I didn't get all that info i'm afraid - however - as the water pressure to the cylinder and top floor shower/taps have remained unchanged, the plumbers who've been in already feel that the water pressure is good, certainly not poor enough to be good flow upstairs and a tiny trickle downstairs! Cheers
Depends whether the downstairs cold is fed directly as you would expect or from the top floor balanced pressure point. That would change things. Especially if the pressure is only just enough to overcome the height and the resistances involved.
Does the cold to downstairs come from the top floor (does it rise to that valve first)?
Is there a NRV on the cold to the top floor?


I am only thinking out loud here as I obviously haven't seen the job but they way it is described brought this to mind as a possibility that's all.
 

scott_d

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Add a lever valve to each cold supply pipe and the hot pipe
Someone else mentioned the cold that tees off after the PRV could draw warm/hot water, move this tee.
Remove the Non return valves if they are not needed.
 

Timmy D

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Just repeating this as it is a valid concern. Out of all the unvented systems I’ve seen, with the info I have, this has got to be at the top as far as legionella risk is concerned.

The cylinder cold inlet needs a non return after all the tees etc, close to the cylinder.

To prevent legionella, stored hot water should be at 60c.

Legionella multiples between 20c-45c.

If the cylinder is set at 60c, the bottom of the cylinder (near cold feed) will not be at 60c. Depending on size/usage etc, it could be closer to 45c.

The non return stops this lower temp water being drawn back in to the DCW system. At present, it could be drawn out of the kitchen tap and drunk.

If you’ve got a hot water recirc line, this also helps reduce the risk as the water in the tank is circulated ensure an even/full temp across the cylinder.

If you don’t have a recirc line, you can add an anti-stagnation pump between tees from hot outlet and cold inlet.
 

John.g

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This would have been easier to install, instead of all the NRVs?.

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ShaunCorbs

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This would have been easier to install, instead of all the NRVs?.

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But then you loose the 25 year warranty on the cylinder you could move the prv block which has the nrv in tho (far right)
 

John.g

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If the multibloc valve was installed like the attachment, (but with the EV connection unused due to the cylinder air bubble) is this acceptable? or is only one balanced cold allowed off it?.

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Last Plumber

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Yes you can feed more than one outlet off the balanced cold as in diagram.
 

Alexwales

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So a small update - the latest plumber came in and isolated all the pipes to try and find the routing and what is blocked. Unfortunately he couldn't find a solution last night, so our next step is to look under the floor boards etc so find what he thinks must be a faulty check valve somewhere.

I've started prepping for this and I removed the cover under the airing cupboard and noticed the pipe that we're focusing our attention on as the likely issue (2nd pipe from right off the T junction with check valve that is now an isolating tap) was labelled: "C-SH-S".

So I tried the cold only on the showers in the house (1st and 2nd floor) and found that if I isolate the 3rd pipe from the right and keep the 2nd open, the shower stays on and visa-versa. Almost as if they're in a circlular set up? Does that make any sense at all? Or they're both plumbed into each shower which seems odd.

Anyway - in the process of all of this, I managed to somehow get the cold to work again in the house, at about 50%, but seemingly constant. I then went back to repeat the process to see if I could improve the flow further, but has now stopped again.

So i'm now left thinking, could there be some sort of flow issue caused by the set up 'sequence' that can have a negative affect on the flow? (Balanced cold water system)

I'll put this all to my plumber when I speak to him, but thought i'd throw it out here in case it makes any sense at all?!
 

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ShaunCorbs

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Yes as if it is both connected they could be both backseating there own check valves if you close the blue lever valve do you get water ?
 

Alexwales

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Yes as if it is both connected they could be both backseating there own check valves if you close the blue lever valve do you get water ?
See attached photo - with the blue mains supply switched off on far left and the far right red lever open, the shower continues to run on the cold.

If I close the red lever, open the far left blue switch and open the blue lever 3rd from right, cold water flows again to same shower.

EDIT - Although is it possible the flow is just coming back from the hot water cylinder?
 

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Alexwales

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Just repeating this as it is a valid concern. Out of all the unvented systems I’ve seen, with the info I have, this has got to be at the top as far as legionella risk is concerned.

The cylinder cold inlet needs a non return after all the tees etc, close to the cylinder.
The current set-up is pictured above - should there be a check valve on the pipe from the cylinder?
 

ShaunCorbs

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I’ve just had a thought is the red lever the mains into the cylinder cupboard and they’ve put the cylinder kit on the wrong pipe ?
 

ShaunCorbs

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But you have mains water coming through back on the red one eg turn the blue one off and open a shower and you still have cold only ?
 

Alexwales

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But you have mains water coming through back on the red one eg turn the blue one off and open a shower and you still have cold only ?
Correct - water flows through into the showers. So either that pipe is also connected somehow to the mains or it's water flowing back from the cylinder into the pipe with the red lever? It's running through cold for the minute or so I tried it, but presumably if it's the water at the bottom of the tank it's likely to be cold as the boiler won't have been on to heat what has been re-filled.
 

John.g

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Is the "RWC 8, 4 bar" (far right) a PRV (pressure reducing valve) and if so, why apparently a waste pipe off it?, or is it a ERV (expansion relief valve) but connected at both ends???.
 

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