Incoming water pressure 5.5bar

[vala]

Had an ASHP survey last week and engineer tested the pressure and flow from the mains.

incoming pressure is 5.5bar so he noted a PRV should be installed.

I'm happy to install one straight after the mains stop cock, however should I install a strainer before the PRV? 

[Conor]

Maybe.

 

Pro: longer PRV life

Con: likely to get clogged and reduce flow over time. Regular cleaning needed.

 

In water networks, strainers cause more issues and cost than they save. Primarily because once they are fitted, they are forgotten about. Hidden. Don't provide a day to day function, and no telemetry giving any idea of condition or functional performance. If you do fit one, set a reminder on your calender to clean it every 6 months.

[John Carroll]

I think most of these PRVs incorporate a strainer which, from what I read, can be almost impossible to remove for cleaning, so maybe install a upstream strainer.

[Nickfromwales]

On 26/07/2026 at 07:38, vala said:

Had an ASHP survey last week and engineer tested the pressure and flow from the mains.

incoming pressure is 5.5bar so he noted a PRV should be installed.

I'm happy to install one straight after the mains stop cock, however should I install a strainer before the PRV? 

Why?  
 

The new UVC will have a PRedV on the control group, therefore all your cold feeds will become balanced at 3bar by default.

 

I’d keep the 5.5 and tee off it for all the WC’s, the washing machine, dishwasher, outside tap (anything significant which just takes a solo cold feed), and then let the PRedV at the UVC do everything else for all the mixing outlets which require balanced supplies. 
 

This is what I am doing atm for a client, with an accumulator on the mains immediately prior to the control group. 

 

Sounds like you found a muppet here tbh, as there’s absolutely zero need to put a PRedV inline immediately before another one?!? . If you do as I suggest above then showers will be as least affected as possible; eg they can take from the full bore mains so these cold feed items won’t then be robbing pressure from the post 3bar side when you least want them to. 

[Nickfromwales]

1 minute ago, John Carroll said:

I think most of these PRVs incorporate a strainer which, from what I read, can be almost impossible to remove for cleaning, so maybe install a upstream strainer.

Standard PRedV on the control group will come with a stainless gauze filter.

 

I always try to put these at eye level and easily accessible so the maintenance is a doddle.

[-rick-]

1 hour ago, Nickfromwales said:

Why?  

 

Is there a water softener?

 

1 hour ago, Nickfromwales said:

I’d keep the 5.5 and tee off it for all the WC’s, the washing machine, dishwasher, outside tap (anything significant which just takes a solo cold feed), and then let the PRedV at the UVC do everything else for all the mixing outlets which require balanced supplies. 

 

Not sure I'd trust modern appliances (or the flexible piping/connections) to be robust (long term) against 5.5 bar. At least check the manual of them.

Edited 14 hours ago by -rick-

[vala]

Thanks for all the replies.

 

@Nickfromwales I'll strike him off the list for our ashp then!

I'll make sure to have it tee'd off before the control group for the ground floor appliances as checked and they can all take in excess of 5.5bar according to their respective manuals. First floor I have a hot and cold water manifold so will leave these as balanced coming off the control group as most are mixers.

[Nickfromwales]

9 hours ago, -rick- said:

 

Is there a water softener?

 

 

Not sure I'd trust modern appliances (or the flexible piping/connections) to be robust (long term) against 5.5 bar. At least check the manual of them.

How many washing machines are sold each year in the UK? And how many of these have someone raise their hand to halt proceedings, stating "I need to check the pressure first!". I'd say that's <20% if that.

 

WRAS stuff is tested to 10bar, and dynamic pressure is very different to static, so some diversity remains here; the reason washing machines / dish-washers et-al don't just blow up all over the place. I used to fit domestic appliances each evening for an appliance showroom, for beer money, and I can't recall any such failures tbh.

 

Almost nobody reads the MI's before installing an appliance, we're a rare few on here, plus most installers are against the clock so simply don't GAF. 

 

Agree, softeners throw a curved ball here, good point. 

[-rick-]

1 minute ago, Nickfromwales said:

WRAS stuff is tested to 10bar, and dynamic pressure is very different to static, so some diversity remains here; the reason washing machines / dish-washers et-al don't just blow up all over the place. I used to fit domestic appliances each evening for an appliance showroom, for beer money, and I can't recall any such failures tbh.

 

Fair, though I didn't initially put my point across as clearly as I should (later edited to mention the pipes but still maybe that's not clear enough). I've both experienced personally and know people who've had leaks caused by the connections between the appliance and the fixed plumbing. That is the element that I'm most suspicious of and it's an age related issue.

 

In my mind the lower the pressure the less likely there is to be a problem and for most appliances pressure is not really required to be high. If the washing machine takes another minute or two to fill who cares? So for me, if building new and lucky enough to have a high pressure feed (around here people are complaining about <1bar, thankfully not affecting me) then I would intend to feed the appliances off a separate PRV from the DHW one.

[Gus Potter]

5 minutes ago, Nickfromwales said:

and dynamic pressure is very different to static

Great point Nick. Often we get what we call "water hammer in pipes" this is where there may be a bit of air, or occasionally pipe lengths that deflect. It sets up an oscillation in the "instant" water pressure ( potentially can exceed normal working pressures by a long way) that can destroy sensitive modern systems. over stress pipe connections. 

 

On 26/07/2026 at 07:38, vala said:

however should I install a strainer before the PRV? 

I would for all it costs. 

 

[Nickfromwales]

26 minutes ago, Gus Potter said:

Often we get what we call "water hammer in pipes" this is where there may be a bit of air, or occasionally pipe lengths that deflect. It sets up an oscillation in the "instant" water pressure

A lot of people mis-diagnose water hammer.

 

Picture the wall of the pipe, over say 20m, it gets pulled (quite violently if it's a good mains) in the opposite direction when the water shoots through it, then when the water gets abruptly shut off the reverse happens. A clunk when it gets going, and a much worse one when it is told to stop. Hence the term "hammer".

 

A simple resolve is to fit a water-hammer arrestor at the incoming stopcock as an accumulator (so dissipator) of said energy. Example here:

 

https://www.screwfix.com/p/flomasta-vessel-shock-arrestor-1-2-bsp/905FA?tc=YT5&gclsrc=aw.ds&gad_source=1&gad_campaignid=19822796606&gbraid=0AAAAAD8IdPwbFYTzmJVQor27lqW3HlWdF&gclid=Cj0KCQjwg5zTBhCLARIsAP2AFU4mo_FATJ9q8AnAmVKo36-pIGsoGKt9BSlS3DhWw4HT_ahp1HefyRoaAoOGEALw_wcB

 

People don't see such problems, if you're not an experienced plumber then you wouldn't, and then have to resolve them somehow, retrospectively and crudely, which is where folk with experience shine through and save such annoyance / cost with some simple mitigation by design.

 

Prob is, good people seem to be few and far between.

[Nickfromwales]

49 minutes ago, -rick- said:

If the washing machine takes another minute or two to fill who cares?

That is not my point here. Nobody cares about how long that takes as far as I know.

 

The way I plumb peoples homes is so that the filling washing machine doesn't rob them of a good blasting shower.

[-rick-]

9 minutes ago, Nickfromwales said:

The way I plumb peoples homes is so that the filling washing machine doesn't rob them of a good blasting shower.

 

100% agree on that. Appliances shouldn't be on the DHW PRV.

[Nickfromwales]

20 minutes ago, -rick- said:

 

100% agree on that. Appliances shouldn't be on the DHW PRV.

"You may pass....." lol