HW Pressure falling after 3 years. Where's the problem? Please help

[Andrew Fish]

Hi Team,

I moved into a new build in 2014 and the HW pressure and flow to all taps over the last 3 years has been good. Recently the HW flow rate has fallen gradually to the point where you can no longer really run a bath at an acceptable flow. The initial pressure on opening any HW tap is good but after a few seconds fades to a low flow. The CW is not affected and has good pressure and flow.
All hot taps are affected.
The water enters the building via a pressure reducing valve on which there is a gauge which reads 3.5 bar static pressure.
There is a water softener in the utility room but when this is by-passed no change is noted to the poor flow of the HW taps.
On opening a CW tap the pressure gauge under the sink in the utility room falls to about 2 bar during flow and when the CW water tap is turned off it immediately returns to 3.5 bar.
When the same is done on a HW tap, the pressure falls to be about 2 bar also, but on closing the HW tap the pressure takes longer to return to the 3.5 static pressure reading.
The mains feeds to an unvented Albion cylinder via a Caleffi 2 bar pressure reducing valve which is used to balance the cold water to the cylinder and the cold supply to all showers and mixers.
I suspect there is something on the HW side which is obstructing the flow and am wondering if it's something to do with the Caleffi PRV? Do these fail with the symptoms I am seeing? I don't know of anything else, like a blocked filter, in the circuit which could be causing this problem.
I have attached a picture of the layout which may help.
Any ideas?
Thanks,

AJ

 

[jtsplumbing]

Has your in a new build you may have blending valves near the hot taps and these need to be serviced may be dirty filter or they need adjusting.

 

[Andrew Fish]

There is a blending valve on the bath I believe, but all the HW taps are affected. Presumably any blending valve fault would only affect the taps it's fitted upstream to?

 

[ShaunCorbs]

Have you had the unvented cylinder serviced?

 

[Best]

I instantly thought same, - get the unvented unit serviced and this will sort your problem.
Unvented units need serviced once a year by a G3 unvented qualified plumber to keep units warranty of (usually) 25 years, but also to keep them functioning 100% and more importantly to have them working safely. They are potentially dangerous

 

[townfanjon]

Snap ^^^ , probably

 

[SimonG]

Should have an annual service.

 

[Jim Goodenough]

I notice the braided hose from the combi valve to the expansion vessel dips down, this contravenes regs - have the UHWS unit serviced now and annually as suggested previously by the pro's.

 

[sammathias]

I notice the braided hose from the combi valve to the expansion vessel dips down, this contravenes regs

Is that correct?

 

[Jim Goodenough]

Is that correct?

Yes, did G3 training recently and instructor taught us flexi-hose from combi valve must rise all the way to vessel - reason being water could possibly stagnate / legionella risk.

 

[townfanjon]

Yes, did G3 training recently and instructor taught us flexi-hose from combi valve must rise all the way to vessel - reason being water could possibly stagnate / legionella risk.

Theres always talk about this on vessels but I have never heard that...

 

[sammathias]

Yeah did my resit 6 months ago and have never heard such thing. They change the regs constantly!

 

[ShaunCorbs]

yea they need to be hard piped now

not that it will affect me as i hate the flexis on them

 

[sammathias]

Dont effect me either, just bash a combi in, job done .

 

[Jim Goodenough]

there was a bloke on the course who says he uses a 22 x 22 x 3/4FI compression tee and screws the vessel straight into the tee - thought that was a great idea.

 

[ShaunCorbs]

there was a bloke on the course who says he uses a 22 x 3/4FI x 22 compression tee and screws the vessel straight into the tee - thought that was a great idea.

yes and no depends where the cold feed enters and if you have enough space and normally like them at/ teed in at the control block

also wouldnt dream of supporting the vessel with just 22mm (not that i think he means that)

 

[Andrew Fish]

Hi Team,

I moved into a new build in 2014 and the HW pressure and flow to all taps over the last 3 years has been good. Recently the HW flow rate has fallen gradually to the point where you can no longer really run a bath at an acceptable flow. The initial pressure on opening any HW tap is good but after a few seconds fades to a low flow. The CW is not affected and has good pressure and flow.
All hot taps are affected.
The water enters the building via a pressure reducing valve on which there is a gauge which reads 3.5 bar static pressure.
There is a water softener in the utility room but when this is by-passed no change is noted to the poor flow of the HW taps.
On opening a CW tap the pressure gauge under the sink in the utility room falls to about 2 bar during flow and when the CW water tap is turned off it immediately returns to 3.5 bar.
When the same is done on a HW tap, the pressure falls to be about 2 bar also, but on closing the HW tap the pressure takes longer to return to the 3.5 static pressure reading.
The mains feeds to an unvented Albion cylinder via a Caleffi 2 bar pressure reducing valve which is used to balance the cold water to the cylinder and the cold supply to all showers and mixers.
I suspect there is something on the HW side which is obstructing the flow and am wondering if it's something to do with the Caleffi PRV? Do these fail with the symptoms I am seeing? I don't know of anything else, like a blocked filter, in the circuit which could be causing this problem.
I have attached a picture of the layout which may help.
Any ideas?
Thanks,

AJ

View attachment 32878

If anyone is interested in the solution to this issue, the problem turned out to be a faulty valve set. In the attached picture you can see the plastic non-return valve which has come free from the housing. It should be located where the red arrow is shown. Clearly it was loose and every

time HW was called for it moved and partially blocked the exit. Pretty poor that this can happen on something that's only a few years old.