Dealing with excessive mains water pressure

[Ricirv]

My apologies for a long initial post...

We have always had a problem with high mains pressure. A particular bugbear is an 8 bar CWS relief valve into an unvented Megaflo that lets by regularly. It happens every other day since its' replacement with an 8 bar relief valve by a G3 certified plumber last week - he'd tried a 6 bar one that failed within the week around Christmas. He said that if this was still a problem then a PRV should be fitted to the tank and bathroom CWS. This has been done (I'd had one before but not liked the noise) by me and the running pressure has been set to 3 bar which is great for the bathroom taps. However, and this is my question, when a downstream tap is shut off, the pressure gauge on the PRV - which reads the outlet pressure - winds slowly up to 7 bar and beyond - extrapolation suggests 9 bar or more. I had assumed that the PRV would shut off once the set pressure (in this instance 3 bar) was exceeded. Does this mean that it is faulty, or is there another way of dealing with high static pressure in a domestic CW system? I'm just a bit fed up with constant dripping from the pressure relief pipe and it freezing up in winter - then backs up to the tundish and all the fun that flows from that. I also know that May Gurney's fitters had an awful time fitting water meters with the high mains pressure round here with sudden floods and small lakes in the roads in the last year. On the positive side the showers are wonderful and the bath fills in no time at all!

Before you suggest it, I have regularly reformed the bubble in the Megaflo as advised by Heatrae Sadia. The plumber said it was definitely the CW inlet valve that was at fault.

 

[sherbert]

I would suggest that your Pressure reducing valve maybe faulty

Have you tried putting a pressure test on the hot somewhere on the system .. it should be about 3bar

If not then change the valve

Sherbert

 

[RichieHoneybucket]

You need a G3 unvented ticket to work on Unvented Cylinders, sorry but Joe Public can't DIY a job like that.

 

[Ricirv]

You need a G3 unvented ticket to work on Unvented Cylinders, sorry but Joe Public can't DIY a job like that.

I am aware of the Building Regulation G3 regarding the unvented cylinder. That is why I called out a suitably qualified and competent plumber as I made clear in my OP. He was unable to fix it despite 2 attempts - as I said in my OP.

I am not aware of a specific regulation regarding fitting a PRV in the CWS upstream of an unvented cylinder - which is why I have fitted it. It does the job very well when a tap is open - but it does not appear to control the pressure if a tap is shut off downstream of it. At least I don't think so...hence my question!

 

[Ricirv]

I would suggest that your Pressure reducing valve maybe faulty

Have you tried putting a pressure test on the hot somewhere on the system .. it should be about 3bar

If not then change the valve

Sherbert

The PRV I installed (nowhere near the cylinder - I am very aware of the limits of my competence and the associated regs) works well and has been set to 3 bar. The reduction in pressure is very noticeable to the WHB, bath and shower. However, once a tap downstream of the PRV is shut off the pressure gauge on the PRV climbs up to and beyond 7 bar and hey presto(!) the inlet relief valve (8 bar) opens and causes no end of irritation. The HW pressure is controlled by a preset 3 bar PRV that is part of the Megaflo but the CWS safety valve is upstream of the Megaflo so it opens regularly - as stated in my OP. Anyway, I have reported this to Anglian Water as the high water pressure in this village is beyond a joke.

 

[RichieHoneybucket]

Sorry mate, I started reading your thread & my eyes glazed over....

Can I suggest you contact a PRV manufacturer & tell them the pressure etc. See what they can do for you as regarding specifying a better valve.

 

[Ricirv]

Sorry mate, I started reading your thread & my eyes glazed over....

I don't blame you - this matter bores me to tears but constant dripping, mossy brickwork, leaking tundish, noisy plumbing and cold water dripping from the ceiling into my breakfast cereal is getting me down.

Can I suggest you contact a PRV manufacturer & tell them the pressure etc. See what they can do for you as regarding specifying a better valve.

Anyone you'd recommend - other than Honeywell (as fitted presently)?

Thanks for your comments

 

[Nige F]

I feel that you need something more than an "off the shelf" prv - I googled and found quite a few UK manufacturers - With that extreme incoming pressure it almost needs something industrial.

 

[Ricirv]

I feel that you need something more than an "off the shelf" prv - I googled and found quite a few UK manufacturers - With that extreme incoming pressure it almost needs something industrial.

I agree. I think it ought to be paid for and installed by the local water company though - in this case Anglian Water. They are the ones causing the problem

 

[picasso]

as a matter of interest does the mains water feed anything else in the house before the prv ? I had a similair problem to yours and it turned out to be the kitchen tap passing (which was plumbed in before the unvented prv) and the back pressure was pressuring the whole system to mains pressure causing the safety valve on the unvented to open.

 

[Ricirv]

as a matter of interest does the mains water feed anything else in the house before the prv ? I had a similair problem to yours and it turned out to be the kitchen tap passing (which was plumbed in before the unvented prv) and the back pressure was pressuring the whole system to mains pressure causing the safety valve on the unvented to open.

My arrangement is similar - The mains feeds the kitchen tap directly and is teed off to an inline scale inhibitor before it tees to the dishwasher and the rising cold water service to the bathroom. The latter branch is where the PRV is installed - ahead of the PRV that is part of the unvented installation.
The system does run at 3 bar as set when a tap is open but rapidly climbs to mains pressure when shut off.

What, may I ask, was the solution in your case?

 

[Gasguru]

Haven't read the posts in much detail but the problems appears to be either...

The unvented pressure reducing valve...it should prevent the pressure downstream rising above the set point. Is this the proper manufacturers valve?

The air bubble has not been formed correctly...sometimes the standard procedure to regenrate the bubble does not work hence rocketing pressures once the cylinder heats up.

The cold tap outlets are directly off the mains (plumb in after the cylinder reducing valve or use a PRV mentioned below) and through let-by are pressurising the hot side.


Be aware that the vast majority of pressure reducing valves available are useless....they will not prevent the downstream pressure from rising up to mains pressure with a no flow condition. They will only maintain pressure during a demand.

Tee in pressure gauges before and after the cylinder pressure reducing valve to help diagnose the fault.

These valves

http://www.altecnic.co.uk/media/k2/attachments/536_PRV_Leaflet.pdf

will maintain the downstream pressure at the set point even with no flow (static condition).

 

[Ricirv]

Haven't read the posts in much detail but the problems appears to be either...

The unvented pressure reducing valve...it should prevent the pressure downstream rising above the set point. Is this the proper manufacturers valve?

This has been undisturbed and as supplied by Megaflo - I am not competent to deal with an unvented system - I left all that to a professional plumber

The air bubble has not been formed correctly...sometimes the standard procedure to regenrate the bubble does not work hence rocketing pressures once the cylinder heats up.

Noted, and thanks for the tip - the last regeneration was done with a warm tank

The cold tap outlets are directly off the mains (plumb in after the cylinder reducing valve or use a PRV mentioned below) and through let-by are pressurising the hot side.

They were directly off the mains but are now off a PRV set to 3 bar


Be aware that the vast majority of pressure reducing valves available are useless....they will not prevent the downstream pressure from rising up to mains pressure with a no flow condition. They will only maintain pressure during a demand.

Quite, I'd noticed that with the PRV fitted to the CWS (it is a Honeywell 15mm PRV)

Tee in pressure gauges before and after the cylinder pressure reducing valve to help diagnose the fault.


These valves

http://www.altecnic.co.uk/media/k2/attachments/536_PRV_Leaflet.pdf

will maintain the downstream pressure at the set point even with no flow (static condition).

Sounds like it is just what I might be after. Thank you for the advice

 

[picasso]

My arrangement is similar - The mains feeds the kitchen tap directly and is teed off to an inline scale inhibitor before it tees to the dishwasher and the rising cold water service to the bathroom. The latter branch is where the PRV is installed - ahead of the PRV that is part of the unvented installation.
The system does run at 3 bar as set when a tap is open but rapidly climbs to mains pressure when shut off.

What, may I ask, was the solution in your case?

isolate your unvented cylinder from the incoming mains, if the tundish continues to drip then its being pressurised from the "hot" side