Low Domestic Water Flow / Pressure - Is it the Taps, Tanks, Pipes or something else

Discussion in 'Plumbers' Talk' started by Stru, Aug 1, 2021.

  1. Stru

    Stru New Member

    Hello, first time poster, long time reader and DIYer here.

    TLDR Output from taps isn't great but cold water seems to be 1.5 Bar, where an I going wrong and what could improve things?

    I'm installing a new kitchen and bathroom in my 120yo flat but I am a bit unhappy with the flow from the taps. There is no gas so I have a gravity fed hot water tank in the loft with a header tank that sits approx 4m above floor level.

    I checked the flow / pressure (sorry I am sure they're not the same thing) by running tap for 6 seconds X 10 = Bar

    Kitchen Sink (15mm approx 6m run from 22mm main supply + stock narrow flexi tails to tap)
    Hot 0.40
    Cold 0.65

    Bathroom Sink (15mm under 1m run from 22mm main + stock narrow flexi tails to tap)
    Hot 0.35
    Cold 0.60

    Bath (22mm on main supply + 22m flexi no tap at present )
    Hot N/A
    Cold 1.50

    Getting 1.5bar on 22mm on a third floor flat doesn't sound terrible but the other taps come off the same pipe and are abysmal despite being rated for low pressure.

    Does anyone have suggestions on how to improve the output from the taps?

    I'm not certain a pump on the hot water supply solves the cold water problems but it's the economical option.
  2. terrymac

    terrymac Screwfix Select

    How many litres of water do you get from the cold tap in the kitchen,when run for one minute ? Your figures quoted above make little sense to me.
  3. pppmacca43

    pppmacca43 Super Member

    To check the pressure you would need to connect a pressure gauge, what you are doing is determining the flow rate in a way.

    I use a flow rate cup, but For you to find your flow rate at home open a tap into a bucket for 10 seconds and then see how many litres u got and times that by six. That will give you the litres per minute.

    The narrow flexis wont help and with a tank only 4 metres up I would expect a very poor flow rate through these. 4 metres of head equals less than 0.4 bar. So if some of your cold taps are off this as well, the pressure won’t be great, although out of the bath tap u would get a decent flow.

    Have you checked all isolation valves and the stoptap are fully open.
  4. Stru

    Stru New Member

    Thanks for the reply and clearing up that this is the flow rate (I wasn't sure!). That would make the values above liters per minute.

    Yes the bath flow prior to starting the project was good and the old bathroom and kitchen taps didn't have the narrow Flexi Tails.

    The isolation / check valves are fully open and the main stopcock is too.

    Are there any options for doing away with the narrow Flexi Tails? The taps are described by the manufacturer as being suitable for low pressure systems.

    Do you know if it's worth adding a pump at the hot water tank and/or on the mains?
  5. pppmacca43

    pppmacca43 Super Member

    What is your kitchen cold tap like? That will(or at least should) definitely be off the mains.
    Adding a pump on the mains might not achieve much depending on what feeds your taps, because your whole bathroom could be tank fed, so all you would be pumping to is pretty much the tank. If everything hot and cold except the kitchen tap is tank fed then a whole house pump might be an option to pump both hot and cold supplies from the tank.
  6. Stru

    Stru New Member

    See original post for length of run from msins. Unfortunately vit's pretty much the same. The kitchen supply was recently run as it was relocated from another room. Its a very simple setup in the flat
  7. pppmacca43

    pppmacca43 Super Member

    I think you need to ascertain what pressure you are getting on the mains, being three storeys up and in an old building with (potentially) old pipes it could be poor, at least then you know what you have coming in. Although high pressure doesn’t necessarily equate to good flow rate.
    I assume your taps with the flexis are monobloc mixer taps and I bet they are either quarter turn or have a single cartridge, which if so will deliver poor flow when used with a tank fed system with only 4m of head.
    Options could include a pump, on the tank fed supplies, or converting the system to mains pressured hot water via a combi or unvented cylinder(if pressure/flow rate is good enough).
  8. Stru

    Stru New Member

    No gas so no combi I'm afraid but you are spot on re the building. Not something that crossed my mind when buying of course.

    The mains connection goes through two other flats before it reaches mine and still has parts in lead... Some mornings it can be too low to run my electric shower. The cold supply is direct on the mains without a header tank and the route is the most direct, lengths off the 22mm route in the original post. Had the floors up and walls open so have seen it all. Just hot water tank is gravity fed.

    I think you're right about the monoblock taps. "monobloc mixer taps and I bet they are either quarter turn or have a single cartridge" is there anything I can do to change the cartridge or is there a particular type of tap I should get?

    Looking online there are mains booster pumps, I don't know if they are particularly reliabile or suitable for my situation of course but open to suggestions
  9. DaveF

    DaveF Active Member

    I would be wary of taps described by the manufacturer as anything!
    I didn't read all of the posts so apologies if I am jumping the gun. You can sometimes find true low pressure taps and often they have two tails just for the hot to provide the flow where there isn't any pressure.
    There are some good quality ( quiet ) booster pumps designed specifically for what you need. Checkout Grundfos. They are darned expensive but excellent. You can boost your cold and your hot but that would be expensive!!
  10. pppmacca43

    pppmacca43 Super Member

    I’ve only ever fitted one booster that goes straight on the mains and that was years ago so can’t really comment on how good they are for you, and like I say, that isn’t going to solve your hot water issue so you would need another pump for that.
    The electric showers we fit at work require at least a bar to operate or they shut down, so possibly at times you are getting less than that.
    The best taps for tank fed are ‘normal’ style taps with tap washers, that can be opened fully. The problem with these modern quarter turn taps is the openings are tiny so the flow through is poor unless you have good pressure pushing it through.

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