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Plumberpro
Plumberpro, Plumber
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Experience:  Heating and plumbing answers. 20 years experience
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hi, fully pressurised system,3.5 bar. When drawing off water

Resolved Question:

hi,
fully pressurised system,3.5 bar.
When drawing off water to ground floor bathroom,hot pressure is greater than cold then cold runs slow and causes slight air in cold tap in upstairs bathroom.
Any ideas,
regards
peter
Submitted: 3 years ago.
Category: Plumbing
Expert:  Plumberpro replied 3 years ago.

Plumberpro : Hi , need a but more info , you say you have a high pressure system . Do you mean an unvented system , ie a mains pressurised cylinder?
Customer:

yes

Plumberpro : Hi . Is the cold supply to the bathroom mains pressure aswell ?
Customer:

yes,after the pressure reducing valve

Plumberpro : Is the pressure reducing valve serving the feed to the cylinder?
Customer:

yes

Plumberpro : Ok . So you have the pressure reducing valve , then after it splits off to hot and cold , sorry to over emphasise it
Customer:

yes

Customer:

ok

Plumberpro : Hi . Do you have anything that would hinder the flow to the downstairs bathroom , ie undersized pipe work of half closed valve?
Customer:

sorry no

Plumberpro : Hello . The cold should split off after the pressure reducing valve(which should be set at 3bar) and before the check valve . Is this right on your system ?
Customer:

sorry yes

Plumberpro : You said the water pressure was at 3.5 bar. This should be 3 bar. I can only assume there is a fault on the pressure reducing valve. The cylinders and pressure vessel act as a boost to pressure and this may be over powering the cold . I have had this before and it was confusing , but changing the pressure reducing valve solved it . Would recommend Thisbe done
Customer:

hi,

Customer:

hi

Customer:

hi,a 3.5 bar prvalve was supplied as part of the pressure vessel kit.the main pressure into the property is 4 bar ,we know because we have checked it,sorry its a bugger

Plumberpro : Is the problem at every tap in the bathroom .
Customer:

yes,two side x side en suite barhrooms upstairs and just the one down stairs,all the same problem.to try to help, the new fully pressured system was fitted in a small room on the same level as the two upstairs bathrooms as the boiler was originally on the ground floor kitchen,does this help?

Plumberpro : Hello . I'm assuming all the pipe work is 22mm 3/4 inch . Was a flow rate check done on the mains cold to an outlet point?
Plumberpro : The minimum flow rate should be around 22litres per minute
Customer:

yes we put the metre on the incoming main and its 4 bar

Plumberpro : No , not the pressure , the flow rate. You can have the same pressure in a pipe a metre wide or a hairs width wide, but the flow rate in volume will be hugely different. With an unvented system the mains pipe should normally be upgraded, as if the flow rate has to be high enough to operate properly . Is it a new system ?
Customer:

as you can see its 4 bar but we havnt checked the flow rate but its a good pressure

Plumberpro : Hello . Was the incoming mains pipe upgraded when the system was installed?
Customer:

no but its 25 mm blue into the house then 15mm copper then 22mm copper to first floor,i can easely check flow rate by time it takes to fill a 10 litre bucket,what

Customer:

25mm blue into house then 15mm copper up to first floor then into 22mm copper.shall I run off 10litres into a bucket to check flow and time it?

Plumberpro : Yes that's a good idea , also how easy would it be to bypass the 15mm copper and take from 25 mm to 22mm copper all the way .
Customer:

no,because 15 mm stop cock and concealed by tiles,will do the flow rate check as we speak

Plumberpro : Ok
Plumberpro : Let the water run for a minute to let the internal pressure realease from the system
Customer:

hi,drawing off in the utility room which is 3m from main and 15mm .10L took 33 seconds

Plumberpro : Did you let the tap run for a while first to let the built up pressure release?
Customer:

yes 15litres,ie 3 gallon bucket,tipped away then checked a new fill,33s for 10L

Plumberpro : I'm sorry but your house has a big system 2 ensuites and a bathroom.plu kitchen . The main has to be kept at least. 25 mm / 22 mm copper all the way . Because could you run every tap in the house at the same time. This should be the design requirement with pressure and flow to spare . I can only recommend a re think on size of the main along the whole route . I know this is rarely an easy job , but I have to be honest with you .
Customer:

thanks,but the system did work ok 3 months ago,thats why we cannot understand it.one small point,if my wife doesn't use the g floor bathroom I do not get air in my top bathroom,if as normal she baths first, in the top bathroom I have a small splurt of air on the cold

Plumberpro : What kind of bath tap is it .
Plumberpro : Air would indicate a loss of water or pressure . Is it a lot of air , is it gurgling and how long for ?
Customer:

three quarter bath mixer taps,monnow taps basins

Plumberpro : Are the taps thermostatic ?
Customer:

no

Customer:

cold spurts when I open tap which splashes up as if under pressure

Plumberpro : Can I ask what happens if you run the bath taps fully , do all the taps run upstairs ?
Customer:

opened bath taps downstairs,no water in my bathroom upstairs,r we getting there now?

Plumberpro : Yes . The flow rate is too low . There is not enough to keep the whole system full .
Customer:

ok,but why has it worked in the past?

Plumberpro : Could you have a leak on the main ? Do you have a meter . Could you turn off all taps and see if the water meter keeps going ! Have a suggestion .the easiest solution would to limit the flow to the bath taps , could use flow limiting valves or gate valves closed off slightly
Customer:

will check the water meter right now

Plumberpro : Ok
Customer:

all ok metere not moving

Plumberpro : Ok . It still boils down to not enough flow . There is usually a filter in the check valve , could this be blocked ?
Plumberpro : Or do you have a filter / strainer on the main!
Customer:

no,but we have checked valve for hot water and its ok.

Customer:

no filter on main

Plumberpro : Could there be a filter on the pressure reducing valve?
Customer:

is it relevant,the hot is more pressure than the cold

Customer:

prvalve,no

Plumberpro : What unvented cylinder is it ?
Customer:

centre store,is this plumb centre? it has its own separate pressur vessel

Plumberpro : How long ago was it installed ?
Customer:

about 2 years

Plumberpro : Ok . Are the bath taps new?
Customer:

no

Plumberpro : There are no valves including outside that could have been closed slightly
Customer:

no

Customer:

note,when we checked the incoming main an hour ago it was turned down a little on the first stopcock

Plumberpro : It all points to a low flow rate buy if you hadn't said it had been ok for two years then I would have said pipe work undersized . Now all I can think is there is a fault on the pressure reducing valve or check valve . I would recommending replacing both .
Customer:

ok,i will do that asap,thanks.

Customer:

can I still contact you through this system,peter

Plumberpro : Your welcome , all the best , Toby
Customer:

thanks,will be in touch,p

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