Low pressure from un-vented cylinder - faulty PRV?

[amuiphoto]

Hi Everybody,

I have a question about water pressure coming from my Gledhill stainless lite 250L unvented tank. The tank was installed around 2 years ago and I was never completely satisfied with the performance of the 2 showers and bath filling.
Today I bought a water pressure gauge and took readings at the kitchen tap and also at the shower head. At the ground floor kitchen I was getting 2.8 bar but at the first floor shower hose the pressure was only 0.8 Bar. Further investigation revealed the pressure on the cold inlet side of the gledhill tank was the same as the shower ie 0.8 bar, the tank is situated on the first floor next to the master bathroom and shower.
Flow measurements (using a 10L bucket) from the shower give a result of around 13 litres per minute at the kitchen tap and the same from the shower mixer.
Would I be correct to assume their is a fault with the PRV and this is causing the mysterious loss of 2 bar from ground floor to first floor, and replacing it would improve pressure at the shower head?

Thanks in advance for any help/advice .

Angus.

 

[Boilerman2]

The PRV will have a Strainer (Filter) built in get this out and clean it
then check pressure/Flow rates again.

 

[amuiphoto]

Hi Boilerman2, thanks for your reply! Have just taken it out and had look, it didnt appear very dirty, but gave it a clean anyway.Taken new readings and 1 bar upstairs and 3 bar at the outside tap so no real improvement unfortunately. It's a combination valve btw.
Cheers.

 

[Agile]

Its not possible for the same pipe system to have 1 Bar downstairs and 3 Bar upstairs or vice versa!

You are talking about a "shower" which mystreriously turns into a tap downstairs!

Even thought of calling a competent plumber?

Tony

 

[amuiphoto]

Thanks Tony, yes I have thought of calling a plumber but am just trying to understand the problem a little better, and if there is actually a problem, the shower does work after all.
Just to clarify, the incoming main comes from the cellar in 22mm and tees off to the kitchen tap in 15mm then continues upstairs to the cylinder in 22mm.
Would the difference in pipe diameters cause the pressure difference?
Thanks,
Angus.

 

[Agile]

Pressure and flow can be related but are different entities.

You have only mentioned pressure.

A 15 mm tube 100 miles long will still have the same pressure at each end when there is no flow. It would not give much flow though.

An unvented needs a 22 mm or larger supply pipe.

Tony

 

[amuiphoto]

The flow is 13 l/min as mentioned in the original post. Pipework is 22mm to the gledhill tank and tee'd off in 15mm to the kitchen tap. These are the locations I'm taking my measurements from and still don't understand why there is a relatively similar flow rate from the shower and the kitchen tap but vastly different pressure reading - any help would be greatly appreciated!!!

 

[MJN]

Its not possible for the same pipe system to have 1 Bar downstairs and 3 Bar upstairs or vice versa!

Who said anything about a 'same pipe' system? The downstairs tap could be straight off the mains, and upstairs (tank and subsequent shower) fed via the PRV.

Even thought of calling a competent plumber?

The problem there is that those you think should be competent often turn out to be anything but.

Angus, is your PRV adjustable? If so, have you tried adjusting it to see if it will allow a greater downstream pressure? (They are usually set to 3 bar and so should not be playing much role in your case but if it's set too low...)

Mathew

 

[amuiphoto]

Thanks for the reply Mathew, and yes I agree, trying to find a competent plumber ain't easy!

The PRV is a fixed cartridge type set at 2.25 bar which is in a combination valve with connections to an expansion vessel etc.

Today I measured the pressure in a number of places and the results are as follows:

Outside (back garden) tap: 4 Bar
Dishwasher tap (kitchen): 2.5 bar
Washing machine tap: 2.5 bar
Shutoff valve to the gledhill tank (first floor) before combo valve/PRV): 2.25 bar.
After combo valve (i.e. at entrance to gledhill cylinder) 1 bar
Shower head (first floor): 1 bar

Flow reading at kitchen tap was 14 L/min
Flow reading at shower head (from thermo mixer shower) 12 L/min
I also removed the pipe (22mm) from the stopcock in the cellar and there was a decent torrent flowing in to my bucket although I couldn't measure because I didn't have a converter for my pressure gauge to 22mm.

Conclusions are that there are 2 problems, the first is that somewhere downstairs I'm losing 1.5 bar demonstrated by the different readings on the outside tap compared to the washing mahine/dishwasher taps. Unfortunately I can't access any of this plumbing without ripping up floor tiles, taking out a stud wall and removing half the kitchen cabinets.

Second problem is the combi valve/PRV - going in is 2.25 bar and leaving is only 1 bar which then goes in to the gledhill tank and subsequently the showers and bath - you get out what you put in and I'm only putting in 1 bar.

Therefore my plan is to tee off the 22mm main in the cellar and run a new 22mm pipe directly to the tank cupboard on the first floor. Secondly I'll replace the combi valve/PRV. Hopefully this will enable me to achieve the full 4 bar, more or less, to the first floor cylinder and then have the performance from the system which I think it's capable of.

Will let you know how it goes.

Cheers,

Angus.

 

[Dan Robinson]

Sounds like your street pressure is 4 bar and the outside tap is simply plumbed onto that before the run to the unvented cylinder.

Your cylinder pressure reducing valve does appear to be faulty.

 

[amuiphoto]

That's what I reckon too. There have been 3 "competent" plumbers worked on the house since the renovation and at least one has made a right royal f..k up... and none have spotted the low pressure problem!

Correction, 4 plumbers have done work on the system, no 1 installed it and left saying it was all fine - didn't want to know about any issues. No 2 installed wet underfloor heating in kitchen and didn't see any problems, no 3 installed heatmiser zone system... Also didn't pick up any problems, and no 4 did a service on the unvented tank and also didn't spot any issues.

What do ya make of that Agile Tony!

 

[simond]

This is almost certainly the PRV/Combi valve failing. Even dirt in the filter would not cause a static pressure drop, unless it were blocked completely, which we know is not the case.

The only other possible reason for the pressure and flow drop is the cylinder discharging to waste, trust you've checked this. Some new builds we've seen have an invisible blow off connection, so no one is any the wiser. Against regs but when you pay peanuts etc.......

I don't know what Tony means when he says you can't have two pressures, that is what a PRV does. It was invented for that purpose.

I may have misunderstood the OP, but the Combi valve must be replaced with the same type exactly. The G3 conformance is based on the safety devices and raising the pressure through the cylinder could be very messy and potentially dangerous. Some cylinders have copper primaries for better heat transfer and these can be damaged by higher pressures.

 

[amuiphoto]

Hi Simon, thanks very much for your reply. I've checked the discharge pipes and there's nothing coming from them so I'm pretty sure it's the combi valve which is at fault.

Been on the phone to Reliance Water Company tech support today and they inform me that a pressure drop of 0.5-0.7 bar across the valve is normal. I'm actually getting a drop of 1.6 bar so have ordered a replacement.
The cartridge currently fitted is set at 2.25 bar but Gledhill have told me I can fit a 3 bar instead, and according to RWC this should constrict less than the 2.25 bar.

Will let you know when I have the new one installed.

Cheers,

Angus.

 

[amuiphoto]

Ok, problem solved... Combi valve replaced and static pressure has increased from 1 bar to 2 bar in master shower and from 0.2 bar to 1.8 bar at 2nd floor shower. Bath fills more quickly too.

Thanks to everyone who contributed there knowledge!

Angus.

 

[MJN]

Nice one Angus!