Posting a message to the forum will remove the above advertisement
  1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.
  2. Checkout our Plumbers Insurance area - heavily discounted Public Liability Insurance and Van Insurance specifically designed for plumbers.

Discuss recent hotwater pressure drop to shower pump - help! in the Bathrooms, Showers and Wetrooms area at

  1. Big_Al

    Big_Al New Member

    Hi everyone,

    I am a DIYer so please be nice! I bought an old house a few years ago so it's an existing set up. I have an ensuite that is fed hot water from a tank downstairs with a CW tank in the loft. So there are pipes that branch off to feed a twin impeller Aqualisa pump, both hot and cold feeds respectively.

    The pump recently packed up, it was a 2bar one. Pressure from it was ok and hot water flow / mix was good. Found a replacement with similar pipe connection config but was rated a bit higher - 2.5bar. Was second hand but looked new - owner said it had hardly been used - I opened it up and impeller / casing inside was pristine, like new.

    Fitted it and re tuned the cold and hot water supply and worked fantastic. Much higher pressure and brilliantly hot showers...etc. Was in my Mrs' good books :) (finally!)

    This shower bliss lasted for about 4 weeks when we noticed that there seemed to be at least a 30% drop in pressure and it seemed that the cold water pressure was overpowering the hot. I tried to retune the supply to the pump - with the hot valve fully open and the cold tuned down but it gets to the point now where, just to make the shower kick in, the minimum pressure from the cold feed still overpowers the hot feed on max....resulting in a tepid, underpowered shower. Out of the Mrs' good books :(

    I stripped the mixer valve ( an old solid Mira thermostatic one, I believe) and soaked it in some descaling stuff, scrubbed it bright and clean. I also adjusted the valve to allow a greater hot water mix and then put it all back together. It seemed to allow more hot water to be mixed, turning it from tepid to warm...but at reduced pressure. This lasts for about 3 minutes or so and then it seems to starve the pump and the pump starts switching on and off every few seconds.

    If I turn the mixer valve on the shower tap to cold - it bursts into life and the shower head jolts back with the pressure and runs fine....but ice cold. I turn it back to the max heat setting on the dial and the water turns warm, pressure reduces and then the pump starts the on off ...on off stuff.

    Hot water supply to the tap in the wash basin in the same en suite, from the same main feed (pretty much) is scalding hot and seems to come out with some force, but have no way of objectively knowing if it is the same as it was, when the shower & hw flow to that, was all working properly. The hw pipe feeding the shower mixer tap is sclading hot.

    If I open the cw feed (as well) to the pump to max, the pump will run at pretty good pressure all the time.

    So it seems to be just that HW feed to the pump that has reduced in pressure, for some reason.

    Any suggestions as to where I might start to sort that out!

    Many thanks for taking the time to read this. Much appreciated.
  2. rpm

    rpm Trusted Plumber Top Contributor!!

    Filter on inlet to pump clean?
    Pipes to the pump correct size?
  3. Big_Al

    Big_Al New Member

    Thanks for the reply. There are no filters on this pump on the inlets - perhaps there should be but didn't notice any when I fitted it. As mentioned in my post, the pump worked brilliantly for about a month before the big drop in pressure. I just tested the pressure to the kitchen tap and it's just over 3Bar so good strong feed coming into my house. Total descale is necessary of all my whole system then do you think?
  4. rpm

    rpm Trusted Plumber Top Contributor!!

    Wouldn`t descale yet. Now thinking it is to do with the hot water side of the pump as it is pulsating. What make is the pump?
  5. Big_Al

    Big_Al New Member

    Its a 2.5Bar Aqualisa twin impeller
  6. Big_Al

    Big_Al New Member

  7. rpm

    rpm Trusted Plumber Top Contributor!!

    Well the Mach has a PCB and 2 reed switches but don`t know enough about them to advise you.
  8. Big_Al

    Big_Al New Member

    Never mind - thanks anyway!
    • Like Like x 1
  9. Big_Al

    Big_Al New Member

    A quick update. I noticed a bleed screw on the hotwater feed to the pump, located after the adjustment valve. I opened it and I heard a hissing noise until water started comming out and then closed it. Seems to have done the trick!

    Hot water and pressure appears to have been restored to my beloved shower! So there appears to have been an air lock in the pipe. I hope this helps someone else in the future.
  10. rpm

    rpm Trusted Plumber Top Contributor!!

    Nice one! Hope it doesn`t return now.
Similar Threads - recent hotwater pressure Forum Date
Performed my first few practicals recently, any tips on the following? Plumbing Forum Oct 2, 2018