Pressure Reducing Valve limiting mains water pressure why?

ecswtrav · Sep 23, 2015

Hello,

I was hoping someone could answer a query that has puzzled me for a while and nobody has been able to help all that much. I have a new mains water supply coming into the basement which has replaced the old lead version. This new connection is instantly greeted by a pressure reducing valve set at just over 2 bar on the meter. My boiler is an ideal iStor (unvented cylinder bolted on to a condensing boiler) - they don't have a good reputation - but this one has caused me very few problems over the past 3 years as its serviced annually. Up to now it works just fine.
Anyway, my showers and taps aren't exactly bursting with power/flow/pressure/ or whatever the technical phrase is. In fact, its no different to the old lead supply. However, I decided to adjust the PRV with a screwdriver and turn the pressure up to see what happened. Instantly the water comes flying out of the taps/showers with some force etc - just how I'd like it. I instantly brought it back down to 2 bar though.
I Wondering what the purpose of this device was, I read the Ideal istor manual and it says this must be installed as the boiler cannot operate on more than 2bar of mains pressure. In fact, the actual boiler comes with the valve when you buy it so it seems.

Why on earth would anyone want to restrict their mains pressure like this? Is there anything I can do to take advantage of having a new mains supply with extra pressure?

I assumed maybe the meter on the PRV was knackered and not giving the correct reading? It could be set at 1bar but showing just over 2? I did notice it reduced in pressure when a tap is switched on - I assumed it would be a constant 2 bar?

Anyway, any advice I'd be very grateful. Thanks

Sparkgap · Oct 1, 2015

ecswtrav said:
sparkgap that's really helpful thank you. The annual service is done by a big insurance company and the last bloke didn't have a clue what the PRV was! I even had to explain it! From the new mains - literally where it joins the house - is this PRV. From what you're saying can I assume this is in the wrong place as it seems from this setup the entire house must be limited by this. I assumed from the diagram inside the installation booklet it was in the right place. From what you're saying the PRV should be situated further upstream before the boiler cold inlet and a seperate mains supply leading elsewhere? Is my setup 100% incorrect or would there be an obvious bit of pipe routing that would confirm all is ok? I've ordered a JET PRV with a clear indicator of pressure and I'm going to have a go of fitting it myself when it arrives to see if maybe the old one is clogged up and not working how it should be. I'll let you know how I get on. thanks

Ideally, fit the PRV on the cold feed to the Istor. The separate cold feed to any shower or mixer valves should come off after the PRV as well to give a balanced supply. Everything else in the house should be directly off the mains and not the PRV.
If the servicing bloke doesn't know what the PRV is for and how to service it then WHAT THE **** IS HE DOING TOUCHING THE SYSTEM AT ALL? The Istor O&M booklet shows how to remove the PRV and clean the filter so this would be the first place to look.

AWheating · Oct 1, 2015

pressure does not equal flow rate, get a proper engineer to service the valve/ set up, if its faulty then get the engineer to change it for the correcty type. it may simply need cleaning out.

the reason the pressure is limited is for safety and correct operation of the safety controls which all need testing on the service.

ecswtrav · Oct 6, 2015

Just a quick update - thanks for all who have helped out. Had a neighbour install the PRV this evening set at 2 bar as recommended by Ideal - he's a mutliskilled fella but not a boiler specialist. The PRV installed is a JET model with a simple way of setting it to 2 bar.
Flow has increased by a litre a minute or so but its still far below the 35lpm indicated in the boiler blurb and the 11lpm supposedly on a depleted tank - I dont get 11lpm on a full tank in the hot tap next to the boiler!
I couldnt help but look at the mains where it enters the house. Can anyone explain why the mains enters the house with a big new plastic pipe which seems to be instantly reduced to 15mm. This then attaches to the PRV which then has a copper pipe leaving to the boiler on 22mm. Could this be restricting flow? Can anyone shine any light on this?

is any new mains connection instantly reduced to a 15mm pipe?

Sparkgap · Oct 8, 2015

ecswtrav said:
Just a quick update - thanks for all who have helped out. Had a neighbour install the PRV this evening set at 2 bar as recommended by Ideal - he's a mutliskilled fella but not a boiler specialist. The PRV installed is a JET model with a simple way of setting it to 2 bar.
Flow has increased by a litre a minute or so but its still far below the 35lpm indicated in the boiler blurb and the 11lpm supposedly on a depleted tank - I dont get 11lpm on a full tank in the hot tap next to the boiler!
I couldnt help but look at the mains where it enters the house. Can anyone explain why the mains enters the house with a big new plastic pipe which seems to be instantly reduced to 15mm. This then attaches to the PRV which then has a copper pipe leaving to the boiler on 22mm. Could this be restricting flow? Can anyone shine any light on this?

is any new mains connection instantly reduced to a 15mm pipe?

No, it's reduced/expanded to whatever size you want! Have you got a pressure gauge on the outlet of the PRV? (Assuming so if you've managed to set it to 2 Bar) How does the pressure in the system change when you open a cold tap? If it drops too much then the problem is your incoming supply. If not then it's in the Istor or your pipework. For a house though I'd be looking at least 22mm pipe or larger for the incoming.

Chris_Swansea · Oct 8, 2015

In simple terms the pressure reducing valve keeps the cold mains supply at no more than 2bar, the pressure relief valve is set at 6bar on unvented systems leaving 4bar for expansion in to cold water main before 6bar prv blows off into discharge pipework, a expansion vessel rated for the system is also added and normally charged at 3bar to help accommodate this expansion. But lets not forget the main reason that only competent persons install/service/repair is that 1ltr of water is turned into 1600ltrs of steam should hot water vessel fail,
and as for replacing the pressure reducing valve most installers fit unvented systems as kits, as all components are suited for that system, so should only be replaced with the same part that was fitted.

ShaunCorbs · Oct 8, 2015

Chris_Swansea said:
In simple terms the pressure reducing valve keeps the cold mains supply at no more than 2bar, the pressure relief valve is set at 6bar on unvented systems leaving 4bar for expansion in to cold water main before 6bar prv blows off into discharge pipework, a expansion vessel rated for the system is also added and normally charged at 3bar to help accommodate this expansion. But lets not forget the main reason that only competent persons install/service/repair is that 1ltr of water is turned into 1600ltrs of steam should hot water vessel fail,
and as for replacing the pressure reducing valve most installers fit unvented systems as kits, as all components are suited for that system, so should only be replaced with the same part that was fitted.

slightly wrong but close all depends on what your system/ boiler is rated to if the cylinder is only rated for 2 bar and the expansion vessel should take any expansion that is needed due to heat up