Shower Pump Pulsating

Discussion in 'Plumbers' Talk' started by seftonbarn, Dec 4, 2018.

  1. seftonbarn

    seftonbarn New Member

    I have added a shower pump to the hot supply to a mixer shower. The mixer shower is a Mira and is about a year old. It had worked fine but wasn't very powerful. The shower is in a bungalow and supplied by a gravity fed system. On initial testing the new pump installation was a success. But now it is temperamental. The shower output pulsates and correspondingly the pump is kicking in and out (on for a second off for a second). I can stop the pulsating in one of 2 different ways: 1. by removing the shower head. And 2 by turning the temperature up to it's hottest setting and then slowly reducing the temperature back to the required temperature. But the next time the shower is used the problem returns. Any ideas or advice as to how I can overcome the problem would be greatly appreciated.
  2. Allsorts

    Allsorts Well-Known Member

    Did you fit a Warwick/Surrey/Essex flange in you hot water cylinder top outlet?

    This is a common issue and is down to the 'triggering' flow for the pump being borderline. Lots of things can cause this such as there not being enough 'head' in the CWS, the wrong type of pump being chosen (+ve and -ve head types), it being located incorrectly, plumbed incorrectly, pipes too small, etc.

    The 'pulse' is the pump firing up drawing a quick slug of water which is the system is struggles to provide from the hot tank so draws the water column down the vent pipe instead, the column hits a low point before bouncing back up which 'pulls' the water flow back from the pump, the pump shutting off due to this suddenly reduced water flow, the water column then hitting the high point so normal flow is restored, the pump firing up again, the pump drawing a slug of... you get the idea. If you could see the water in the vent pipe, chances are it's bouncing up and down. (It can also happen with things like the hot cylinder wall flexing.)

    If you don't have a flange fitted in your tank, then this can exacerbate the situation; this might be enough for a cure.

    Failing that, we'd need to know the pump type, where it's fitted etc.

    Is there any room to raise the CWS height?
    seftonbarn likes this.
  3. Hans_25

    Hans_25 Active Member

    Per Allsorts, could be air in the system.

    Also somewhat confused as you say you've fitted a pump to the hot water, what about the cold water feed, what's the pressure of that? Cold and hot feeds need to be the same pressure.
    seftonbarn and Allsorts like this.
  4. just pumps

    just pumps Active Member

    Single pump to hot side only?
    seftonbarn and Allsorts like this.
  5. seftonbarn

    seftonbarn New Member

    Thanks to Allsorts/Hans_25/Just Pumps for your input. May I respond to all of your inputs in one.
    Firstly thank you to Allsorts for your creditable explanation of a possible solution. I acknowledge that is more complex than I had first thought. I am not a plumber and don't fancy taking on the fitting of a Warwick/Surrey/Essex flange. Though I understand how that could possibly resolve the problems associated with a "borderline triggering flow".

    To respond to Hans_25 and Just Pumps - rightly or wrongly, yes I have just added a pump to the hot water side of the shower. My thinking was that the gravity fed cold system would be sufficient. I also acknowledge that the mixer requirements specified is for hot and colds of equal pressures. My research prior to this led me to the "plumber chap" on You Tube who implied in one of his videos that it was acceptable to boost just the hot side of the mixer (but I also acknowledge that the said "plumber chap" also recommend the fitting of an Essex Flange).

    For now I have reverted said shower back to gravity. By coincidence I am also fitting a new shower in another part of the house. My plan initially is to see how that gets on with just boosting the hot.
  6. Heat

    Heat Well-Known Member

    Unvented cylinder (installed by someone qualified in unvented work) if you have good enough pressure and flow rates is best.

    Or a combi gas boiler if you haven’t too much a water usage (ie - not ideal for several bathrooms and large occupancy) and if mains flow and pressure is also okay.

    Or a quality twin pump (Stuart and Turner) to do both the cold and hot for showers would be good. Also have to consider if negative or positive head pump required.
  7. DIYDave.

    DIYDave. Well-Known Member

    Vastly unequal pressure between the hot and cold feeds usually plays havoc with temp control on a thermostatic shower

    So apart from the pulsing issue, your unlikely to have good temp control

    What made you go single impeller pump ?
    seftonbarn likes this.
  8. Allsorts

    Allsorts Well-Known Member

    Yeah - rub it in, Dave, why don't you :)
    seftonbarn likes this.
  9. Pollowick

    Pollowick Well-Known Member

    If you are doing two showers, and provided they are not in use at the same time, you could use a good high quality pump to feed both of them. And take the time to get a flange or second take off installed - have a careful look at the cylinder as you may find a blanking cap on the side where a take off can be added.

    I personally have mains cold and stored hot (blame the plumber that did the original install) which I had to upgrade with a pump on the hot. It can feed both showers at once - although the flow is slightly down on both but fully acceptable and the hot water runs out!
    seftonbarn likes this.
  10. seftonbarn

    seftonbarn New Member

    Thanks for the input. I didn't go for a single pump; I already had a twin pump which was only used on one side to boost the pressure to a monobloc kitchen tap. So I thought I would use the redundant side to boost the shower. If I turn the temperature up to its hottest setting and then very slowly wind it back to a comfortable temperature it works perfectly. But that is a bit of a pain. I am going to get ask a plumber to fit a Warwick/Surrey/Essex flange in my hot water cylinder top outlet and see how that goes.
  11. Allsorts

    Allsorts Well-Known Member

    Turning it to hot max gets the hot flow running strongly and smoothly, so the water column I mentioned before quickly levels out and stops bouncing. Then you can back off the hot slowly and the column just gently rises to its new level - but doesn't overshoot and go in to pulses.

    That's my theory and I'm sticking with it...

    I think the flange is the best first step - chances are it'll sort it. If not, ask him about the wisdom of connecting that twin pump to boost both H&C to the shower so it's more balanced.
    seftonbarn likes this.
  12. seftonbarn

    seftonbarn New Member

    Thanks. Yeah; that sounds logical. I will let you know how it goes.
  13. Pollowick

    Pollowick Well-Known Member

    Have you checked for any unused outlet on the side of the tank?

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