Cold water flow problem has stumped 3 plumbers...can you help?!

[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

 

[Scott_D]

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]

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]

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

 

[ShaunCorbs]

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

View attachment 75334

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]

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?.

 

[Last Plumber]

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

 

[Alexwales]

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?!

 

[ShaunCorbs]

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]

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?

 

[Alexwales]

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]

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 ?

 

[Alexwales]

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 ?

I've just checked, no the mains is the blue switch/PRV pipe on the left.

 

[ShaunCorbs]

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]

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]

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???.

 

[ShaunCorbs]

Is the water hot ?

Also need to run it a bit longer under 5 mins

 

[John.g]

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???.

Seems to be a form of block valve but not a ERV, lifts at 8bar ("mains") but incorporates a NRV. (no bearing on current problems).

 

[Last Plumber]

I know I asked this before but there was no reply.

Does the cold rise to the top floor then feed the lower floors?
What is the mains pressure at the ground level?

I know it might seem a silly question but to my mind, this is getting too complicated. You need to rule out the simple things first.

 

[John.g]

Be handy now that all have lever valves to label them individually and text briefly explaining what floor etc they are supplying.

 

[Alexwales]

I know I asked this before but there was no reply.

Does the cold rise to the top floor then feed the lower floors?
What is the mains pressure at the ground level?

I know it might seem a silly question but to my mind, this is getting too complicated. You need to rule out the simple things first.

Our understanding is yes, it does rise to the top before heading back down.

I don't know what the mains pressure is, but one of the first things we did was get welsh water in and they checked it and said the flow was good into the house.

As far as I know the pressure is OK, none of the other technicians have been concerned about it, it seems adequate enough to flow well on the top floor and fill the cylinder as normal.

HOWEVER - the plot thickened this morning - I woke up and went to the kitchen and for the first time in 5 weeks the cold taps were suddenly running at 80/90% power. I left them running for 4/5 mins, no stop in flow. I went the the bathroom next door, the taps worked. I left the tap running and flushed the toilet, the tap slowed to about 30/40% but kept going.

I had to pop out and when I came back, it was still working at this slightly reduced level. So I went around and checked everything that hadn't worked and it was working. 30 mins later, it's all stopped again.....

So this slightly dispels the blockage theory and seems much more a pressure issue, right? I suppose there could still be a faulty PRV somewhere behind a wall, but it seems unlikely it would just randomly start working again?

 

[Alexwales]

Be handy now that all have lever valves to label them individually and text briefly explaining what floor etc they are supplying.

This is what we know so far. As yet, we've not been able to work out which line feeds the rest of house: I.E Kitchen, cold in bath, bathroom sink and toilet, ground floor bathroom sink and toilet and outside tap.

 

[John.g]

This is what we know so far. As yet, we've not been able to work out which line feeds the rest of house: I.E Kitchen, cold in bath, bathroom sink and toilet, ground floor bathroom sink and toilet and outside tap.

If all flows reduce proportionally then points to pressure issue, can't understand why a pressure gauge seems to be a rarity on most unvented systems which depend solely on mains pressure, the PG can tell such a lot.

You might also consider shutting the red lever valve "also showers" as the cylinder "ERV" above it will prevent back flow when the cylinder heats up and also prove that this valve is orientated correctly as there will be no cold water supply to the cylinder if not.

 

[Ben-gee]

This erratic behaviour could be explained by faulty/sticking non-return valves, quite possibly fitted the wrong way around.

These have plastic parts inside and operate against a spring, I’ve had damaged ones where the ‘mechanism’ gets jammed sideways and moves around a bit. Ended up with a hand full of bits we I removed it all. Replaced with a new one and problem solved.

 

[Alexwales]

This erratic behaviour could be explained by faulty/sticking non-return valves, quite possibly fitted the wrong way around.

These have plastic parts inside and operate against a spring, I’ve had damaged ones where the ‘mechanism’ gets jammed sideways and moves around a bit. Ended up with a hand full of bits we I removed it all. Replaced with a new one and problem solved.

Thanks - yes this is what my plumber thinks os the issue - the problem is that we've replaced/removed all the 'visible' NRV on the system (as pictured) and still the problem remains.

So we're left with the nightmare (and expensive) task of lifting chipboard/going behind walls etc to see IF there is one hidden away somewhere randomly...and we're talking behind fully tiled walls in a bathroom that is 7 years old, so all bonkers really.

 

[Alexwales]

The only part that's not been changed is in the yellow circle.

Does this have a check vale built in that could be faulty?