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

 

[John.g]

Yes, this has a check valve but even if faulty or the valve has been installed wrong way round, the cylinder will still be supplied from the shower supply (which in shouldn't), just shutting that red lever valve will prevent this and also prove that the cylinder is being correctly supplied.

Personally, before doing anything more and in view of flows back to normal this morning, I wouldn't spend another cent but I would go away and invest in a £10 pressure gauge that you yourself can screw on to your outside tap and observe it for a few hours or so, its so simple and basic to do this IMO.

 

[gpbeck]

Any neighbours with the same house? If so, any had problems?

 

[Devisham]

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.

From the updated pictures this is still relevant and hasn't been ruled out yet to my knowledge. Relocate the PRV to the correct position, install a single check valve in the correct position on the cylinder inlet and remove the other multiple check valves not required. The PRV in its current position is restricting the overall system and with the multiple NRVs not needed as well as being installed in sequence the flow is being further restricted.

 

[Alexwales]

Any neighbours with the same house? If so, any had problems?

Yes! I put a note in every neighbours house - 2 came back to me.

One with EXACTLY the same issue several years ago, after 4 weeks (and several visits from plumbers) the problem disappeared by itself - so not ver helpful for us.

Second with either the same or a similar issue that was fixed by reversing the check-valve i've had removed - not worked for us though yet - although we are having one or two sporadic periods of it working in the last few days since that valve was taken out.

 

[Alexwales]

From the updated pictures this is still relevant and hasn't been ruled out yet to my knowledge. Relocate the PRV to the correct position, install a single check valve in the correct position on the cylinder inlet and remove the other multiple check valves not required. The PRV in its current position is restricting the overall system and with the multiple NRVs not needed as well as being installed in sequence the flow is being further restricted.

Thanks for this - I think before anymore exploratory work i'll ask them to do exactly this next.

 

[Alexwales]

Yes, this has a check valve but even if faulty or the valve has been installed wrong way round, the cylinder will still be supplied from the shower supply (which in shouldn't), just shutting that red lever valve will prevent this and also prove that the cylinder is being correctly supplied.

Personally, before doing anything more and in view of flows back to normal this morning, I wouldn't spend another cent but I would go away and invest in a £10 pressure gauge that you yourself can screw on to your outside tap and observe it for a few hours or so, its so simple and basic to do this IMO.

The water pressure is a consideration - although as mentioned before none of the technicians felt it was an issue - I don't have the necessary tool, nor a suitable plug to fit it on (outside tap is one effected by this low/no flow).

My bathroom taps have built in aerator things - so I tried the bit rudimentary method of taking the hose of the shower mixer tap, and filling a jug of water on just the cold setting - it blasted out well over a litre in 6 seconds. Although I don't know if that how accurate that test would be if through the mixer there is some cylinder water pressure, even turned to full cold?

 

[John.g]

The water pressure is a consideration - although as mentioned before none of the technicians felt it was an issue - I don't have the necessary tool, nor a suitable plug to fit it on (outside tap is one effected by this low/no flow).

My bathroom taps have built in aerator things - so I tried the bit rudimentary method of taking the hose of the shower mixer tap, and filling a jug of water on just the cold setting - it blasted out well over a litre in 6 seconds. Although I don't know if that how accurate that test would be if through the mixer there is some cylinder water pressure, even turned to full cold?

10LPM isn't a bad flow from shower cold only, you could just measure flow rate with shower at its normal temperature setting and while this will be the sum of hot+cold flowrates, it still reflects the total mains cold water flowrate. If this is normal, say, 12/15LPM and if the downstairs flowrate is still very poor immediately after completing this test then it would appear to be a internal problem.

However, in view of you and your neighbour...... "One with EXACTLY the same issue several years ago, after 4 weeks (and several visits from plumbers) the problem disappeared by itself - so not ver helpful for us." I would get your plumber to now install a (permanent) PG say on top of that manifold to remove all guesswork re fluctuating mains pressure, or not.

 

[Alexwales]

The latest situation, if this makes any sense to anybody:

The cold water has started, sporadically, to work again, for short periods of time, at pretty much full power. Long enough on one occasion to fill 6 litres of water bottles, so i'm 99% sure it was running freely from the mains.

But it will then lose flow again and stop if you turn the tap on and off.

So I've worked out 2 things:

1) that the taps with low/no flow downstairs are actually linked to the second cold line from the left (pictured) which is the pipe that also does the upstairs sink and toilet, which has worked fine throughout this issue.

2) It seems like (no regular pattern though) if I use the upstairs sink or toilet and run the cold for a bit, it also "kick starts" the flow downstairs, i.e I run the upstairs tap, go downstairs and it will work on occassion.

So presuming this rules out a foreign body block or airlock?

Does this point to some sort of pressure issue? Or a hidden PRV/NRV that is faulty - i.e is somehow being forced open by the upstairs water pressure before closing back on itself?

 

[John.g]

Just try this (but don't know what it will prove!) open the upstairs toilet cold sink then open the downstairs cold until water flows downstairs, let both taps flow and just shut that red lever valve and see if both flows stop.

Should have asked earlier though, is there problems with the d/stairs hot as well??.

 

[John.g]

I see you have no problems with HW supply. You could also try running off some hot water only with a d/stairs cold open and see if this establishes a cold flow, the HW cylinder may be building up a high pressure (due to expansion) in the cold side because effectively no NRV in the system (if the extreme far right lever valve remains open).

 

[Alexwales]

Thanks, I've tried both of your suggestions John, no difference. N.B hot water has remained fine throughout.

The (almost) pattern that has formed is, flush the upstairs toilet and it seems to charge/kickstart the flow downstairs, which stays on until you shut the tap, when the flow stops again.

 

[John.g]

Extraordinary. I have a outside PG and took a few readings just now, D/stairs toilet, normal pressure 3.55bar, 2.85bar after flushing, pressure rose briefly to 4.8bar when fluidmaster filling valve closed, then reduced to 3.55bar. U/stairs toilet with conventional B/cock, no "kickstart", 3.55bar/2.8bar/3.55bar.

 

[Last Plumber]

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?

I would suggest you buy a pressure gauge and take the pressure.
It is possible with the height to the top floor and frictional resistances through pipework, valves, governors and NRV's etc, that you might struggle to get decent flow, especially at peak times.

e.g. If the top floor pipework was say 6 meter above ground, you've already lost 0.6 bar and things like NRV's can lose another 0.1 - 0.3 bar. My thinking is that if you had just over 1 bar incoming, it might struggle. Water authority would look at that pressure as acceptable.

I know there is a descending column of pipework that will help overcome pressure issues in some cases but it depends on the route and size of pipework as well as its component parts.

I am not saying this is the answer but with the fluctuations you have mentioned, I think it needs to be ruled out before you go any further.

 

[Alexwales]

Thank you for all you advice on this - i'm glad to report the issue is finally solved.

Our plumber, through a process of elimination, found the water stopped flowing in a short vertical section of piping from the spare bedroom, down into the main bathroom a floor below.

He cut a hatch in the floorboards and sent some smaller piping down the 'blocked' pipe until it came out the other end...with it came a flush of trapped water, but strangely no obvious foreign body (that we found) and no resistance met (rouge valves) - and that solved the issue.

So we were still left a little stumped as there was no obvious block, but the issue is now finally gone.