Low pressure/low flow

[Simon Read]

Hi All,

I live in a 400 yr old house although the pipework is only 3yrs old from the internal stopcock. I have a low water pressure / low flow problem that I wish to sort out. It's a 25mm incoming pipe stepped down to 22mm internally which then reduces to 15mm into the various taps. I have a PRV with pressure gauge fitted to the system as I wondered what the pressure was. I have a systemic pressure of 3.5bar which reduces to 0.7bar with one tap on. With 1 tap on I get a flow rate of just over 12lpm (only have a 12ltr bucket which fills up in 50sec)

With 2 taps on I get a dynamic pressure of under 0.5bar and a flow rate of 9.5lpm. Both of these taps are downstairs. My problem is that the upstairs electric shower struggles, presumably because of the low flow/pressure. It's a low pressure shower working on a minimum of 0.7bar. Its not too bad until someone flushes a toilet, then it just doesn't recover at all. It has to be turned off until the toilet stops filling then can be turned back on again. The downstairs mains fed shower works perfectly, regardless.

My boiler is an oil fired worcester bosch greenstar.

Is it worth contacting the water board or should I look at a flow pump like the salamander?

 

[SJB060685]

You should look into accumulators and charging pumps. An accumulator does not increase incoming pressure but rather maximises it. Its basically a large expansion vessel that stores pressurised water, when a tap opens it helps maintain working pressure and flow, although these need to be sized correctly. They tend to only supply roughly 50% of stored volume in boost, so a 200 litre accumulator will provide roughly 100 litres before it needs to refill.
The other option is an incoming charging pump. Again these need to installed correctly with a break tank etc.

 

[Simon Read]

You should look into accumulators and charging pumps. An accumulator does not increase incoming pressure but rather maximises it. Its basically a large expansion vessel that stores pressurised water, when a tap opens it helps maintain working pressure and flow, although these need to be sized correctly. They tend to only supply roughly 50% of stored volume in boost, so a 200 litre accumulator will provide roughly 100 litres before it needs to refill.
The other option is an incoming charging pump. Again these need to installed correctly with a break tank etc.

thanks for that, so you think it’s unlikely to be a supply problem to the house?

 

[SJB060685]

Your incoming supply piping is OK I believe and so is your internal pipework of 22mm dropping to 15mm for each appliance. Although large pipework = better flow rates, you still need good pressure and your dynamic is poor as you said. There are several ways around this, 1. Increase supply pipework size to achieve better flow rates, again good pressure is still required, or the above mentioned.
Has this been an issue for some time?

 

[Brambles]

SJB is spot on.

You really need to be looking at a 200 to 400 litre pumped accumulator (circa £1800 installed and commissioned) to solve the problem once and for all.That will give you 4 bar dynamic at 30 litres per minute (until the store runs dry!).

Be wary of using a Mains Booster - they are not always effective nor a long term solution if your neighbours start to fit them too. If you opt for the Mains Booster solution, it needs to be located as close to your water meter as possible and on the same diameter pipe as that upstream of your meter. If not, you are reducing its potential performance before you even switch it on.

A pumped accumulator is only limited by its recharge time, which can be balance by increasing storage capacity.

We design bespoke systems for the Oxon and North London area - where the incoming pressures and flow are particularly low. Never had a dissatisfied Customer, but sadly the solutions are not cheap.

For Thames Water, they regard 0.5bar dynamic and 8 litres/minute as quite acceptable.

Hope this helps

 

[Simon Read]

Has this been an issue for some time?

since our owner ship yea. We moved in 3yrs ago and the plumbing was many years old and leaking lots. Since we were renovating anyway we decided to rip every pipe out and start again. The old system was an unvented system in the loft heated via back burner. We have converted to a combi system. We only used the old set up for about a week so didn’t really have a good time to test it but it didn’t seem much better (could have been due to all the leaks though)

 

[SJB060685]

Brambles and I advice above is all you need to know to consider your options. A sure fire way of improving your situation but like Brambles said it won't come cheap and getting the wrong installer in is likely to make matters worse

 

[Simon Read]

Lovely, thanks to you both

 

[aqualogic]

where is the prv fitted if on incoming main i would remove it

 

[Simon Read]

where is the prv fitted if on incoming main i would remove it

Hi, yes it’s between the main stopcock (inside the house) and the rest of the house? Why would you suggest removing?

Thanks,

Simon

 

[aqualogic]

the prv is probably the problem this will test it

 

[Jim Goodenough]

@Simon Read have look at DAB Esybox and Esytank, 480ltr storage and modulating 3bar pump - I've installed a few and they've worked well. Not cheap unit with be around £1300.

 

[John.g]

Hi, yes it’s between the main stopcock (inside the house) and the rest of the house? Why would you suggest removing?

Thanks,

Simon

Your electric shower will only flow ~ 4 LPM to give a 40C showering temperature, if the mains/PRV cannot supply this, then the PRV is suspect, as above.

 

[moonlight]

Is your pressure reducing valve an adjustable one? a Worcester boiler can have up to a maximum of 10 bar incoming cold water pressure. So adjusting yours up to test might be worth a try first. Make sure all the other appliances can take an increased pressure first.

 

[SJB060685]

I would be cautious about adjusting an adjustable PRV on your incoming mains. Although I can't find a maximum inlet pressure figure in the boiler manual, from personal experience I can say some combis don't react well to a high static or dynamic pressure (I've replaced enough fibre washers and other parts due to failure).
As Brambles and I said, its more likely to be what we've discussed.
A PRV only affects the pressure, one might argue it would reduce the flow rates slightly but doubtful. If you really wanted to be sure though you could isolate the cold mains into boiler and remove the PRV and replace with a short bit of pipe, if your flow rates on cold improve then ok but you would still need a PRV into boiler and then the system won't be balanced anyway.

 

[John.g]

Is there no pressure gauge on the PRV??

Should have read post #1, there is.

 

[Brambles]

Hi,

to get to the to the root cause you need to know the dynamic pressure and flow rate from your unrestricted incoming mains. To do this, isolate your incomming mains at the meter / external stop tap, remove your PRV and insert a pup piece.

Thereafter, measure the dynamic pressure ( when flowing) and flow rate at various times of day ( 9am, noon, 3pm, 6pm and midnight).

That will then give you the base data to develop a solution. If your static pressure (not flowing) is greater than 7 bar then I would reinstate the PRV, if not I would leave it out of the system. If you do have the luxury of a high incoming static pressure - spend plenty of time checking and monitoring the system (particularly compression joints)

My guess is that your incoming mains is the issue and that the PRV is not restricting either the dynamic pressure or flow rate.

There are occasions where high static pressures deliver deliver low dynamic pressure and low flow rates, but usually only on sub 20mm MDPE incommers

 

[Ric2013]

I have had a pressure reducing/regulating valve fail to open properly. It had been fitted in a holiday chalet and seen very little use, so it may have become partially seized for that reason.

The owner of the building had set it to around 1 Bar IIRC and it shut-off correctly at the set pressure, but it would not open up sufficiently to allow any kind of reasonable dynamic pressure. In fact, it even took several seconds to allow the pressure to recover after all taps had been shut.

The solution was to replace the valve and the problem was solved. I did, however, take the old valve home, and was eventually able to free it off. Untested, but it probably would work perfectly now.

 

[Simon Read]

Hi all, apologies for the delay in responding. Took me a few weeks to getting round to removing the pressure reducing valve and then wanted to give it enough time to ensure a good test before reporting back.

We instantly noticed a change in the upstairs electric shower, full temperature control has now resumed and the shower is now far more pleasant to be in. The taps now run faster and I’ve needed to reduce the flow with the stop cocks feeding each tap now. My garden hose flows quicker and my sprinkler now sprinkles rather than dribbles.

Many thanks for all your advice and assistance.

 

[SJB060685]

Hi all, apologies for the delay in responding. Took me a few weeks to getting round to removing the pressure reducing valve and then wanted to give it enough time to ensure a good test before reporting back.

We instantly noticed a change in the upstairs electric shower, full temperature control has now resumed and the shower is now far more pleasant to be in. The taps now run faster and I’ve needed to reduce the flow with the stop cocks feeding each tap now. My garden hose flows quicker and my sprinkler now sprinkles rather than dribbles.

Many thanks for all your advice and assistance.

Hi Simon.

I'm glad that a simple removal of the PRV has improved your situation.
I'd like to point out though that an excessively static pressure can damage seals/washers on a combi boiler, do you know the now static pressure?

 

[Simon Read]

Hi Simon.

I'm glad that a simple removal of the PRV has improved your situation.
I'd like to point out though that an excessively static pressure can damage seals/washers on a combi boiler, do you know the now static pressure?

Hi, I don’t I’m afraid no. The PRV that was on it had a pressure gauge on it. I never saw this go above 3.5bar (static reading) however I’m not sure if it was showing that as the PRV was set to 3bar or wether that was the actual static pressure of the system.......

 

[SJB060685]

That reading is most likely what the PRV was set to allow as maximum.
If its been a number of weeks without problem then touch wood it should be holding.
If you took the front of the boiler off and inspected around the PHX and cold mains pipe that is where you might encounter problems

 

[Ric2013]

That reading is most likely what the PRV was set to allow as maximum.
If its been a number of weeks without problem then touch wood it should be holding.
If you took the front of the boiler off and inspected around the PHX and cold mains pipe that is where you might encounter problems

If the OP isn't a registered gas installer, then probably best he doesn't start taking the boiler apart?
Agreed that the 3.5Bar is probably what the PRV was limiting the pressure to.

 

[Simon Read]

If the OP isn't a registered gas installer, then probably best he doesn't start taking the boiler apart?
Agreed that the 3.5Bar is probably what the PRV was limiting the pressure to.

Hi, no I’m not a qualified plumber. My system is an external oil fired combi system though. I fitted the whole system myself before having it all signed off by a qualified plumber so I’m pretty familiar with the system. I’ve looked and not noticed any leaks at all around the boiler or various other parts of the system 👍🏻

 

[SJB060685]

If the OP isn't a registered gas installer, then probably best he doesn't start taking the boiler apart?
Agreed that the 3.5Bar is probably what the PRV was limiting the pressure to.

In his original posts the OP stated it was an oil combi. If it was a gas boiler obviously I would not suggest removing the cover but as its oil, the fact the OP has already demonstrated a good understanding and the boiler casing has to be removed in order to access the filling loop by the end user im confident the OP could give a quick check of what i suggested without putting himself, family or system in danger.