Water pressure too high even after PRV

[Stealthdude]

Hi all,

A while back we had an issue with our boiler that was covered under warranty. The engineer that fixed it said our mains water pressure was too high and recommended a PRV to be fitted. I bought a gauge and it was reading 13bar, so I fitted a PRV just after the stop cock and set it to 5 bar. However, when checking the pressure on the PRV in the morning it often says it is over 8 bar (off the scale). I read somewhere that a PRV can cause high pressure due to not allowing pressure back to the mains due to temp increase in pipes. So I have now also added a 6 bar pressure relief valve aswell, however the pressure reading on the PRV still reads off the scale in the morning or when I turn the hot tap off quickly. Is there anything else I can do or look at changing?
System is a Worcester bosch combi boiler.

Cheers in advance

 

[CBW]

Maybe contact your water supplier, see if they’ve can’t reduce it. 13 bar seems far too much imo, especially when some struggle to get 1 bar! If you have a system boiler, why is your mains pressure too much?

 

[Stealthdude]

I have tried contacting water board they said if its too high its my responsibility. I'm guessing boiler operating pressure has a limit not sure what atm.

 

[Johntheo5]

Hi all,

A while back we had an issue with our boiler that was covered under warranty. The engineer that fixed it said our mains water pressure was too high and recommended a PRV to be fitted. I bought a gauge and it was reading 13bar, so I fitted a PRV just after the stop cock and set it to 5 bar. However, when checking the pressure on the PRV in the morning it often says it is over 8 bar (off the scale). I read somewhere that a PRV can cause high pressure due to not allowing pressure back to the mains due to temp increase in pipes. So I have now also added a 6 bar pressure relief valve aswell, however the pressure reading on the PRV still reads off the scale in the morning or when I turn the hot tap off quickly. Is there anything else I can do or look at changing?
System is a Worcester bosch combi boiler.

Cheers in advance

What make/type of PRV?, you probably require a drop tight type for that, also most standard PRVs have a maximum inlet pressure of 6bar.

 

[CBW]

I have tried contacting water board they said if its too high its my responsibility. I'm guessing boiler operating pressure has a limit not sure what atm.

3 bar, but that’s system pressure, not related to your incoming pressures

 

[Madrab]

most standard PRVs have a maximum inlet pressure of 6bar.

Most decent PRV's I see available these days are drop tight? 0-16bar input - various (spelling edit) outputs

Set your mains to 3bar - if you are obtaining 3 bar dynamic then your house cold mains doesn't need any more than that, higher the pressure, higher the wear and tear on the appliances/outlets/infrastructure.

If you find you are getting excessive expansion in the pipes, usually down to the fact that they aren't insulated and the water is then warming up and expanding then you could always use a small EV - 2ltr - to absorb that overnight pressure increase.

 

[Stealthdude]

I did have a 'predator' trv from screwfix but changed it to a Hollywell I think as I assumed that that was the issue. If they are only suitable up to 6 bar is there a different one that would suit? If I get an Expansion Vessel is there a specific place it has to be fitted?

 

[Johntheo5]

The Honeywell D06F is good for 16bar inlet pressure and is drop tight.

 

[Madrab]

All the Reliance Predator's are drop tight and are good up to 16bar. Good quality valve.

The EV, can go anywhere on the domestic main after the PRV or any check valve if fitted

 

[Johntheo5]

All the Reliance Predator's are drop tight and are good up to 16bar. Good quality valve.

The EV, can go anywhere on the domestic main after the PRV or any check valve if fitted

It didn't work for Stealthdude?

 

[Madrab]

It didn't work for Stealthdude?

Did it not, or is his issue expansion? All the predator valves are drop tight, that being said, could he also have got a bad one, always possible.

 

[Johntheo5]

Could be expansion especially if his boiler has DHW preheat, some makers now invalidate their warranty if no EV installed.

 

[Madrab]

Yup, wouldn't be the first time I've heard of that. It would also be the case that we would install PRV's to protect the boiler, where the mains pressure was found to be above 3bar.

 

[Stealthdude]

I've actually found just turning the hot water tap off quickly causes the pressure to remain high @ 8 bar. Its possible this is the issue as the other half wouldn't notice if it was too high before going to bed. I can't understand why the relief valve isn't kicking in though as that is rated @ 6 bar. I might just get a 3 bar one to try.

Note I haven't got the predator valve on now, it's a Honeywell one. But has the exact same issue.

 

[Johntheo5]

So to be clear, you have a Honeywell D06F?? PRV installed on the mains supply to the combi boiler, you have a PG installed on the PRV and you have a 6 bar pressure relief valve installed between the PRV and the boiler cold feed inlet?.

When you request HW does the PG fall to (edited) 5.0bar and then rise to 8.0 bar immediately on closing the HW "tap"? if so, then very surprising that the 6bar pressure relief valve isnt lifting, almost unheard of IMO that it wouldn't lift at its design pressure.

Can you post a photo of your set up.

Can you also just open a hot tap to give a trickle of HW (boiler doesn't have to fire up) and see what pressure you get.

If its a mixer HW tap you are opening then its possible that if the cold water supply to this is at mains pressure then its pressurizing the HW system, the PRV should be, if not doing so, installed on the supply to the house. Although if this is happening you would think that the combi mightn't fire up on HW request.