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Using a shower pump for hot only

edited 30 November -1 at 1:00AM in In my home (includes DIY) MoneySaving
8 replies 4.9K views
HorlockHorlock Forumite
1K Posts
I'm wondering whether you really need to pump both the hot and the cold water when you use a shower pump.

The cold water for the bath is currently filled with mains pressure, while the hot water for the bath is currently filled from the storage tank.

Everything I read says that the pumps require you to also pump the cold - but this seems illogical. Obviously perfectly logical if the hot and cold are both fed from the same tank (since if one is low pressure the other will also be low pressure), but in the situation we have the cold has high pressure and the hot has low pressure.

Obviously you can't pump the cold (illegal as well as a bad idea), but I'm wondering about how to fit a pump.

The pump I have has two sides (I only need to use the one!)

As I see it there are a few options.

1. Just connect up one side?
2. Split the hot water on both sides of the pump, and hope that this confuses the pump into working. Eg split 22mm pipe into 2 pipes connect to pump then connect the two outputs from the pump back into one and continue towards the bath?
3. Try to find another pump?
4. Something more sensible that someone here will suggest.
5. Stupid option - Adapt an electric shower and fill the bath with mains water runnering through the adapted electric shower.

So I'm just wondering whether anything will solve my problem for me.
There is no intelligent life out there ... ask any goldfish!

Replies

  • Alex1983Alex1983 Forumite
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    Could you tee the cold into the cold feed for the cyclinder, both hot and cold would then be tank feed and under equal pressure. I'm not a qualified plumber I work on boilers so a plumber may be alone in the minute to say you can't do that.
  • fezsterfezster Forumite
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    Check the pump instructions, but I doubt you can pump just one side using it (certainly, Salamander pumps you can't). If it does work, it may reduce the life of the pump.

    You are allowed to pump the mains up to 12 l/m:

    https://www.emergencyplumber.uk.com/plumbing/mains-water-booster-pump/

    However, again, I doubt you could use a twin pump to pump one side gravity fed, and the other mains fed.

    The *right* solutions are:

    1. Buy a single channel pump to match your mains pressure.
    2. Run new pipework from your cold water tank in the loft to the cold side of the pump.
  • HorlockHorlock Forumite
    1K Posts
    fezster wrote: »
    Check the pump instructions, but I doubt you can pump just one side using it (certainly, Salamander pumps you can't). If it does work, it may reduce the life of the pump.

    You are allowed to pump the mains up to 12 l/m:

    https://www.emergencyplumber.uk.com/plumbing/mains-water-booster-pump/

    However, again, I doubt you could use a twin pump to pump one side gravity fed, and the other mains fed.

    The *right* solutions are:

    1. Buy a single channel pump to match your mains pressure.
    2. Run new pipework from your cold water tank in the loft to the cold side of the pump.

    Thanks for rapid response.

    Could you explain the first *right* solution.

    1. "to match your mains pressure" - why is it important to match the mains pressure?
    I'm possibly being stupid here, but I'm not worried about the two taps having exactly the same flow rate, but it could be there is another reason.

    As far as 2 goes. I think I may have more issues with the second option because the hot water is all 22mm and the cold is all 15mm so it might not prove quite as simple as that.

    But on the other hand if there are single channel pumps then that sounds like it may be the best solution - I just haven't seen any. Then again I didn't have the name to google. Will see what I can find now.

    [I've been given two shower pumps both of which are dual channel and when I googled shower pumps they always seemed to be dual channel].
    There is no intelligent life out there ... ask any goldfish!
  • fezsterfezster Forumite
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    https://www.salamanderpumps.co.uk/pump-selector.php

    Example of a single impeller pump:

    http://www.screwfix.com/p/salamander-pumps-ct55-xtra-1-5bar-regenerative-single-shower-pump-1-5bar/13775

    You want to try and match your incoming cold mains (or even put a pressure reducing valve on your cold main, as it fluctuates during the day) so that your thermostatic mixer is able to function as intended (though it will cope with flow and pressure changes in the 2 inputs to an extent).
  • fezster wrote: »
    https://www.salamanderpumps.co.uk/pump-selector.php

    Example of a single impeller pump:

    http://www.screwfix.com/p/salamander-pumps-ct55-xtra-1-5bar-regenerative-single-shower-pump-1-5bar/13775

    You want to try and match your incoming cold mains (or even put a pressure reducing valve on your cold main, as it fluctuates during the day) so that your thermostatic mixer is able to function as intended (though it will cope with flow and pressure changes in the 2 inputs to an extent).

    OK, that makes sense. I'm not trying to feed a thermostatic mixer, just two taps, but now it makes sense why everyone says the pressure needs to be the same. I literally just want some pressure on my hot water tap in the attic. Currently the hot water tap trickles (since the tank is higher) but that is all - and I can't really raise the tank.
    There is no intelligent life out there ... ask any goldfish!
  • beduthbeduth Forumite
    84 Posts
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    I have a tap in the kitchen which is a long run from my combi boiler. It takes ages for my hot water to come through. Is there anything I can do about this ?
  • fezsterfezster Forumite
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    Horlock wrote: »
    OK, that makes sense. I'm not trying to feed a thermostatic mixer, just two taps, but now it makes sense why everyone says the pressure needs to be the same. I literally just want some pressure on my hot water tap in the attic. Currently the hot water tap trickles (since the tank is higher) but that is all - and I can't really raise the tank.


    If not feeding a mixer, then I wouldn't worry about differing pressures and flow rates. That only comes into play if you don't want the cold to overpower the hot.

    Fit a single impeller pump to the hot.
  • fezsterfezster Forumite
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    beduth wrote: »
    I have a tap in the kitchen which is a long run from my combi boiler. It takes ages for my hot water to come through. Is there anything I can do about this ?

    You either need to:

    1. reduce the pipe length to the tap (only possible if it's unnecessarily long for some reason)

    2. Decrease the size of the pipe (eg. 15mm instead of 22mm). This will reduce flow rate, but being a combi boiler, 15mm will probably still be more than adequate for the flow rate the boiler can manage anyway.

    If you had a tank system, you could fit a hot water secondary return, which pumps water around a circuit on a timer so that hot water is ready to be used during times you have specified. You would need to ensure the entire circuit is well insulated as otherwise this wastes a lot of heat. This isn't possible with your combi system, though.
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