Pressure Pump Hot Only - Mixer Shower

Discussion in 'Plumbers' Talk' started by DIYFirstReno, Jun 29, 2022.

  1. DIYFirstReno

    DIYFirstReno New Member

    If you have a mixer shower with gravity fed hot and cold mains, can you get a pump to pressurise the hot? I have been told that doing this is not good plumbing practice but I do not fully understand why? Can someone explain? Is it possible if you use a negative head/universal pump?
  2. Chris Curwen

    Chris Curwen Member

    The clear answer is..... yes you can get a single impeller pump to supply additional pressure to just one water utility.

    The reason why its not advised, or works in the best formate, is one should really only supply mixer showers with balanced pressures.... ie either both low pressure or both mains pressure (or pressure reduced).

    Therefore, for best performance etc, you need a dual pump device pumping both low pressure hot and cold.

    It means more plumbing in essence, which a lot of end users choose not to have done, (or undertake themselves), as the means of getting low pressure cold water is tricky.

    Low pressure cold (or tanked cold) is the water that feeds your hot storage cyinder tank.
    You may need to breach into the coldp storage tank ( its either above the hot cylinder or presumably in your loft), with a new 'take off'.
    Make sure (if doing such a task), you get a take off point slightly higher than the bottom of the tank base, (say 50-100mm up), to avoid taking sediment from the base of the tank.

    Sedimentation will give you a 'dirty' shower, block filters in the pump and/or shower, and reduce the life of the pump (also known as Booster Pump).

    I would consider a Combination boiler before undertaking this work, unless your means of getting hot water is only via electric immers immersion heating.

    Single impeller booster pumps are also very noisy.
  3. DIYFirstReno

    DIYFirstReno New Member

    Thank you very much! This is really helpful. If a single booster pump was installed to boost hot water against the mains cold, do you/anyone know if another cold mains outlet was opened, would the pressure on cold mains in shower drop?
  4. terrymac

    terrymac Screwfix Select

    You need balanced pressures on hot and cold ,and mains cold and pumped hot is asking for trouble.
  5. DIYFirstReno

    DIYFirstReno New Member

    Thank you, terrymac. I’m trying to understand what trouble it can cause so I can explain to my bathroom fitters.
    Can you explain what might happen? My understanding is that unbalanced pressure might make the shower difficult to work, the cold mains pressure might be affected by using other outlets which could mean the shower gets hotter than expected, and that if the wrong pump is used then it could push back and blow the pump/flood house. Is there anything else I’m missing?
  6. terrymac

    terrymac Screwfix Select

    If your bathroom fitters don't understand the need for balanced supplies to a mixer ,I suggest you don't use them ,you shouldn't need to explain to a qualified plumber ( who you should be using) how to do their job.
    If the supplies are not balanced it won't work, simple as that. Two different pressures are outside the parameters within which a Thermostatic mixer valve can function.
  7. DIYFirstReno

    DIYFirstReno New Member

    Ok, thank you!

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