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low water supply into property fitted with PRV using indirect unvented cylinder

Postby Blackthorn1 » Sat Dec 19, 2020 8:18 am

I live in a new-build 3-bed single storey Bungalow on a new eleven property development in a rural location.

The hot water and heating are provided by a heat pump and an indirect unvented cylinder. The Installation Manual states, “A high static (no flow) mains pressure is no guarantee of good flow availability. In a domestic installation 1.5bar and 25ltr/min should be regarded as the minimum. The maximum mains pressure that the inlet control set can cope with is 10bar.

I have made enquiries with the local water company and it just meets the Ofwat minimum supply standard of a mains pressure of 1 bar and a water flow rate of 9L/min. The highest-pressure reading recorded by me has been 2.25 bar with a flow rate of 16L/min but as soon as a tap is turned on in the property the pressure and flow rate plummets to the lower levels. The pressure and flow rate checks were carried out on the outside tap which is fed just prior to the indirect unvented cylinder.

The water company has informed me that the average pressure in a main is approximately 3 bar. But we definitely do not get that pressure in the building.

The blue mains water supply pipe into the property is 25 mm and comes into the building under the kitchen sink where the kitchen cold tap and dishwasher are supplied.

The cold supply then goes into the attic space where a pressure reduction valve (PRV) has been fitted. From this point onwards all the cold-water outlets and the indirect unvented cylinder are supplied by the same pipework.

We have problems with our hot water supply and the UFH system does not function as it should. This goes for the majority of the eleven 3 & 4-bed properties in the development, especially if they are fully occupied?

Could someone please explain the reason why the developer’s plumbing & heating subcontractor would fit a PRV to the cold-water supply when the pressure is particularly low and where reducing devices could be easily fitted to every outlet (taps & showers)?

I would appreciate any advice?

Thank you
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Postby stoneyboy » Mon Dec 21, 2020 11:48 pm

Hi blackthorn1
You should check your pressure and flow rate from the kitchen tap ie before the prv.
It is far cheaper to fit just one prv bearing in mind they cost around £30.
Regards S
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