Manual mixer shower / pumped hot water / cold water mains

Discussion in 'Plumbers' Talk' started by ColinK, Dec 7, 2017.

  1. ColinK

    ColinK New Member

    Hello All.

    we recently moved into a new property and i've been making some changes to the plumbing.
    the initial problem was that the gravity fed hot water was really really poor.

    So i fitted a 3 bar Salamander pump CT Force 30 PS on the exit from the hot water cylinder (using one of the Salamander S tank flanges).

    This works brilliantly and the hot water pressure is now very good all around the house.
    on the sinks with a separate cold/hot tap I don't have any issues.
    on the mixer taps (bathroom/kitchen) which have a cold water mains feed everything seems to work very well.. both the hot water and cold water mains are under pressure and the mixer taps work fine.

    Our two showers that take a cold feed directly from the cold water tank in the loft and this is under very poor pressure, so the hot water pressure is over powering the cold water in the manual shower mixers and the hot water is back filling the cold water supply back to the cold water tank.

    my initial plan was to take a feed off the cold water mains entering the cold water tank and using that to feed the cold water to the 2 showers as this seems to work well for the bath and kitchen sink.
    however i read that this is not necessarily a good idea as the cold water pressure can fluctuate and cause simple mixer showers to fluctuate in temp.

    is it really such a bad idea to use a manual mixer when the pressures might be dissimilar ?
    would this not just be the same thing as when some herbert turns on the hot/cold taps elsewhere in the house and causes a sudden spike/drop in temp ?

    if its really that bad what the next step ?

    would a set of thermostatic mixers deal with the issue ?

    Cheers in advance for any help....
  2. Is it a bad idea to supply even a thermo mixer with different pressures? Yes.

    I don't know of any mixer that's happy with that arrangement, tho' there might be one.

    Possible solutions is to reduce the mains pressure before the shower mixer so it matches that of the pump - what is it, 2 bar? For this you use a PRV.

    That might work - wait until plumbers come along on here.

    The other is to also boost the cold stored water so that it's increased to match the hot.
  3. ColinK

    ColinK New Member

  4. It isn't very likely to be above three bar, but could be. Circa 3bar is typical, so could be close to what you want.

    Wait for plumbers to comment on whether it's ok since the pressures are close, 'cos I don't know... :oops:
  5. The Teach

    The Teach Well-Known Member

    The showers need balanced water pressure to work correctly and a means of thermostatic control for the prevention of scalding.

    Shower remedy,fit a pump that will pump both hot & cold water from the water storage tank (loft) into individual thermostatic shower mixer valves.

    Pumps and multiple showers can work well but need correct setting up, consideration of an unvented cylinder should not be forgotten.

    Happy plumbing :)
  6. Would a stored hot supply - delivered via a 3bar pump - not work alongside a mains cold also at roughly 3bar to supply a shower mixer??

    The guy already has his hot (only) boosted to 3 bar.
  7. Pollowick

    Pollowick Well-Known Member

    Yes it can.
  8. The Teach

    The Teach Well-Known Member

    It can work well for one shower only as long as the pump is supplying similar water pressure as what is in the cold water mains,there will be variations.
    The shower mixer has to be a suitable item aswell and consider other pumped hot water outlets in operation while showering,the system can be installed and set up to give priority to the shower and with more consideration 2 showers can just about work with limitations.

    Personally we would not install 2 showers where the hot is pumped and cold mains fed but we spend a lot of time rectifying other peoples new installations.
    terrymac likes this.
  9. ColinK

    ColinK New Member

    installed a PRV between the cold water mains (in the loft) and the feed to the 2 showers.
    the pressure reads at around 2.5 bar.
    the pump for the hot water is rated at 3 bar (dropping to 2.6/2.1 bar depending on flow)

    tested both the showers with manual mixers and everything seems to be working as intended.
    neither the hot or cold is over powering the other, there is no back filling going on and temperatures remain constant.
    I get that the PRV isn't actually doing anything, but it reassuring to know what the cold water pressure is, as it could have been 5/6 bar etc.

    Points noted about many things be on at the same time and causing fluctuations in water pressure.
    i will keep an eye on that.

    Cheer for peoples imput.

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