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Discuss Increase shower pressure - unvented system in the Bathrooms, Showers and Wetrooms area at

  1. alexb123

    alexb123 New Member

    Earlier this year we had our en suite refitted.
    Since, the shower pressure is lower than it was previously (not much, but enough to be slightly annoying)
    I think it's down to the mixer - perhaps not as free flowing as the previous
    It’s this - Square manual shower valve

    My question is... Would replacing this mixer be the right thing to do?
    This is all sat behind a single tile (pictured)
    (would have to cut out this tile, replace the plumbing, and replace tile)
    It would also be possible to reach behind this area if needs be through the wall behind it.
    Maybe something like this:
    Grohe Grohtherm Cube thermostatic shower valve

    Or would fitting a shower pump be more appropriate?
    It's an unvented tank. I saw salamander do a pump for unvented systems
    Right Pump 120 SU Pumps | Salamander Pumps
    to ‘force’ more water through the mixer?

  2. steadyon

    steadyon Active Member

    1. Measure the pressure of your incoming cold water. This will give the maximum pressure available via the unvented cylinder. In practice the hot water pressure may be less. You'll need a pressure gauge (Monument?) and possibly an adaptor to fit a pipe or fitting.
    2. Measure the flow in litres per minute from the existing shower. Use a flow cup or measure how long it takes to fill a 10litre bucket and calculate.
    3. The Grohe shower you mention should give a flow of 26litres / minute (lpm) at 3 bar. If you've got less than 1 bar pressure it won't work properly. If you've got between 1bar and 3 bar, then I'd expect about 10lpm at 1 bar and 20lpm at 2bar, but its not strictly in linear proportion.
    4. You could try asking the supplier of the existing shower what the flow should be at your pressure. If you are not getting that flow rate it could be a blocked filter or some other issue, but unlikely as fairly recent installation.
    5. The pump you mention can't be used with an unvented cylinder without installing a break tank
    • Like Like x 1
  3. Ant Parkes

    Ant Parkes Plumber

    In an ideal situation, whoever did the en-suite would take flow rate and water pressure to ensure what fixtures and fittings they quote, are suitable.

    Do you know your current mains water pressure into the house?

    Has anyone messed with the reducing valve that is by your cylinder?

    Is the shower pressure always the same, or can it feel better at different times in the day, say less peak times?
  4. alexb123

    alexb123 New Member

    in fairness - i chose the fittings (with zero expertise in this area)

    Not sure what the mains pressure into the house is -
    The shower pressure in another bathroom (without this mixer) is fine... it just seems to have reduced in the bathroom where this particular mixer was installed - so i'm pointing my fingers at it and calling it guilty
  5. Ant Parkes

    Ant Parkes Plumber

    In this case, contact Victoria Plum on their chat and ask them for a data sheet on the current valve you have installed as you wish to check LPM & Pressure you're getting, against it.

    You'll need a pressure gauge which attaches to say a washing machine tap to check incoming pressure.

    And a weir cup, or as above a bucket and work out litres per minute.
  6. alexb123

    alexb123 New Member

  7. Ant Parkes

    Ant Parkes Plumber

    @alexb123@alexb123 yes mate, grab one of those. Can go on washing machine tap or outside tap.

    It may not be faulty, it may just give you 15 lpm @ 3 bar whereas the other one you linked gives 26lpm @ 3 bar.
  8. SimonG

    SimonG Trusted Plumber Top Contributor!!

    Had your unvented cylinder serviced recently?
  9. alexb123

    alexb123 New Member

    not that I know of...
    It's just suspicious how the showers that don't have the Victoria Plum mixer seem ok (or a lot better)
  10. SimonG

    SimonG Trusted Plumber Top Contributor!!

    That's because anything from victoria/victorian plumb is tat.
    • Like Like x 2
    • Agree Agree x 1
  11. king of pipes

    king of pipes Trusted Plumber GSR

    Are you sure the installer didnt fit a flow restrictor to the shower outlet on the shower mixer most come with one ? Cheers kop
    • Agree Agree x 1
  12. Ant Parkes

    Ant Parkes Plumber

    I did also think this. Most installation instructions / data sheets show a LPM with and without them fitted. However, the valve he has fitted has neither of those readily available on VP. haha.
  13. Chalked

    Chalked Plumber GSR

    Nearly all modern mixers are restricted in some form to give 12litres a minute. The Chinese stuff is normally restricted by having small waterways.
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