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Discuss Mixer tap, bath heats fine, shower fluctuates. in the Bathrooms, Showers and Wetrooms area at

  1. Peter Charlton

    Peter Charlton New Member

    Good Evening,

    Thank you for any help I get forward more.

    I have two problems if you don't mind.

    Firstly, we have had an issue with the shower heat ever after the shower head got replaced, if the head is held above the mixer tap line it fluctuates in heat from very cold to very hot. If you are running a bath off the mixer tap then it works perfectly. The pressure on the boiler is set to the correct bar, the over flow is clear, it is intermittent but not enough to ignore.

    The heating in some rooms works almost OK, the ground floor is heated fine but as you move up through the house its get worse. That's not the weirdest thing, the 3rd floor works fine while the second doesn't.

    Boiler Model: M11032SM/e
    Serial No: M059960707

    Secondly, we have an issue with the ground floor shower flooding with grey water from the 2nd and 3rd floor, is this down to the external pipe angle or how can we rectify this.

    Any help again is more than appreciated.

    Kind regards

  2. Svenedin

    Svenedin Member

    So it's a Combi boiler? Is this related to other people opening hot and cold taps, using the loo etc when you are using the shower mixer? Is it a thermostatic mixer valve or a non-thermostatic type? What is the flow rate like when you hold the shower handset about the mixer?
  3. Peter Charlton

    Peter Charlton New Member

    It is a combi boiler. I wish it was that simple that when someone flushed it got weird, this happens at all times of days, I work nights other work days.

    Please can you clarify to a noob, "Is it a thermostatic mixer valve or a non-thermostatic type?"?

    flow rate is always is the same.

    thanks again

  4. Svenedin

    Svenedin Member

    I should tell you I'm not a plumber just a DIY'er. Thermostatic mixer valves are the type designed to keep the set temperature steady regardless of whether the flow changes in the hot and cold supply. This is done with a thermostatic cartridge inside the mixer. Non-thermostatic mixer valves are simpler and just mix the hot and cold without being able to keep the temperature steady so that if there is a change in the hot or cold supply supply pressure it will either go hot or cold. Is it a bath filler/mixer valve with a shower handset for washing your hair in the bath or actually for standing up and using as a proper shower?
    Last edited: May 20, 2019
  5. Peter Charlton

    Peter Charlton New Member

    Good Evening,

    thank you for your help,


    "Is it a bath filler/mixer valve with a shower handset for washing your hair in the bath or actually for standing up and using as a proper shower?"

    I think it would be a filler, you have a single handle that you turn left to right for hot / cold. you have a little knob in the middle of the tap you lift if you want to have a shower, the hose extends from under the mixer tap to a shower head.

    hope this helps

  6. Svenedin

    Svenedin Member

    Ok. Did it ever work properly? Is this a new problem?
  7. Peter Charlton

    Peter Charlton New Member

    worked perfectly, till a new a shower head was attached, this is what gets me, the bath works fine, the shower dosen't.
  8. Svenedin

    Svenedin Member

    Well that is probably the answer! Some shower heads are "eco" and restrict the water flow. Some years ago I was in Germany and saw a Grohe shower head at a good price. When I installed it, it was hopeless and I had to go back to the old one. If you unscrew the shower head from the hose it is possible (but perhaps unlikely) there may be a special kind of washer in there (called a pcw-01), they restrict the flow to a certain number of litres per minute. If you take that washer out, if fitted, the flow may be greatly improved but be aware that you would need a plain washer to replace it with (very easily obtainable) because the washer will form the seal between shower head and hose. You might also find a washer with a kind of wire mesh strainer which may be blocked with debris or scale or the shower head may need de-scaling. Try the shower with no head attached and see whether the water temperature misbehaves just coming out of the hose which should narrow things down. Incidentally, did you change the hose as well as the shower head? The are not all the same bore, some are narrow and restrictive.
    Last edited: May 20, 2019
  9. Peter Charlton

    Peter Charlton New Member

    Great advice, but have black rings in the base :(
  10. Peter Charlton

    Peter Charlton New Member

    no luck taking the head off :(
  11. Svenedin

    Svenedin Member

    They just unscrew from the hose but it may be tight. You may need pliers to grip the hose where it connects to the head but protect it with a cloth to save scratching the chrome. Sometimes they do have flats for a spanner.

    If you cannot remove the head from the hose but can remove the hose from the outlet of the mixer perhaps try a shower head from one of the others bathrooms or the old shower head if you still have it.
    Last edited: May 21, 2019
  12. Peter Charlton

    Peter Charlton New Member

    If I can be honest, I think its a dead pipe issue. If the bath runs hot and the shower doesn't from the same mixer tap, then why would it happen? Radiators heating in lower floors but not the middle and then going cold. Boilers don't flip out but what do i know :)
  13. Svenedin

    Svenedin Member

    It could happen for any number of reasons. The fact it goes wonky when you lift the shower above the mixer but the bath filler is fine suggests poor pressure (you are asking the water to go uphill from the mixer in basic terms). I was just trying to eliminate the basic stuff first. I don’t know what’s up with your radiators but have you bled them? Are they just full of air?
  14. king of pipes

    king of pipes Trusted Plumber GSR

    Ģo to your boiler and observe what happens when the boiler is in hotwater mode with the shower mixer running , I expect it will be firing up then going off then firing again if this is indeed the case then a GSI will be needed to sort out this issue. Kop
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