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Discuss Varying shower temperature in the Central Heating Forum area at UKPlumbersForums.co.uk.

  1. James Mcdowell

    James Mcdowell New Member

    Background:
    I live on the first floor in a block of 24 flats with a water pressure booster set (this has been serviced and is in full working order).
    I have a Weissmann vitodens 100-w boiler.
    One shower is a Bristan mixer shower, the other is an Aqualisa thermostatic quartz A2 mixer shower.

    Both showers in my flat vary in temperature (and pressure) when in use. I have noticed that when the shower is in use the boiler kicks when required but gets to 88 degrees approx and turns itself off. When the temperature cools down again it kicks back in. So you get hot-tepid-hot-cold-tepid showers. This happens at any time of day.

    The same happens with my hot taps (ie boiler going on and off).

    To complicate things - the water flow to my flat (and others in the block) varies between 8-15L/minute. I have confirmed this with a weir gauge in my own flat and other flats. This variation happens several times over a minute. See attached video in dropbox link.

    I have no plumbing experience but have tried to read up online about this. I have spoken to various plumbers and still no answer. My theories are as follows:

    The boiler works hard to heat the high flow rate of water. When the flow drops it seems to overheat so shuts off (the flame signal on the lcd screen disappears).
    Could the PRV in my boiler have failed?
    Could a temperature sensor in the boiler be faulty?
    Could the secondary heat exchanger could be a problem or blocked? This sounds an expensive thing to fix first.

    Solutions I have thought of:
    Get a PRV on my mains supply so my pressure is more constant - perhaps giving a flow of 8-10L/minute? Would this help the boiler not to fire up SO much and then overheat?

    Further questions:
    Is it reasonable to expect that my water flow is fairly constant? 8 - 15L/min seems a huge variation to expect the boiler to deal with.

    Attached items:
    Dropbox - video.mov
     
  2. dancinplumba

    dancinplumba Trusted Plumber GSR

    you need a GSR to sort boiler out, there is an issue with it.
    pressure should be constant with booster set unless its not big enough
     
  3. James Mcdowell

    James Mcdowell New Member

    I had a British gas annual boiler service approx 18 months ago. This was after I had the above problem and they confirmed that the boiler was working fine. I did mention this problem at the time but they pointed it away from the boiler.

    Could it be they don't (or didn't) check for other problems?
     
    • Funny Funny x 1
  4. dancinplumba

    dancinplumba Trusted Plumber GSR

    yes , probably
     
  5. JCplumb

    JCplumb Plumber

    I have a similar issue with my thermostatic mixer shower on a combi, need to turn the desired water temp on the boiler down to about 55 to stop it happening.
    I'm no gas man but I figured the shower slows the hot down more the hotter it gets so at some points is throttling the hot water enough to make the boiler think it's satisfying temp demand so the water temp then cools until the boiler sees the need to to fire up again.
    Try turning your water dial to 3 on the boiler and see if it still happens.
     
  6. Chalked

    Chalked Plumber GSR

    Annual service 18months ago! :D
     
    • Funny Funny x 2
    • Like Like x 1
  7. James Mcdowell

    James Mcdowell New Member

    Should the boiler be getting up to 88 degrees?
    I tried turning down the water temp but it still goes pretty much as high.
     
  8. JCplumb

    JCplumb Plumber

    Not a gas engy, but when I turn mine down to 55 it doesn't go above 60.
     
  9. johnduffell

    johnduffell Member

    Could be your plate heat exchanger is scaled up so the heat is going into the primary water but not getting to the dhw quick enough.
    Try turning the target dhw temp as low as possible, we use 35c target and turn the hot tap on only. Saves gas anyway that way. But it could be time for a new plate hex anyway.
     
    • Like Like x 1
  10. James Mcdowell

    James Mcdowell New Member

    What do you think about the fluctuations in water flow?
     
  11. johnduffell

    johnduffell Member

    I thought you said that was an issue with the incoming water supply? You'd have to get onto the free holder about that or the water company.
    If forced to guess I'd say there's a restriction somewhere in the pipework upstream of the flats, and there's a header tank that's keeping itself topped up.
     
  12. James Mcdowell

    James Mcdowell New Member

    There is an issue with the incoming water supply. It varies between 8-15L/min on all cold taps. Same issue in other flats on same floor, floor above and ground floor.

    Water company have checked the supply to the booster set. The company that service the booster set have replaced it and recently serviced it. No change. There is not a header tank.

    Where else could the fault be?
     
  13. Harvest Fields

    Harvest Fields Trusted Plumber GSR Top Contributor!!

    You cannot gauge flow from your taps. It needs to be tested from the point it enters the property. All taps let out different flow rates.
     
  14. James Mcdowell

    James Mcdowell New Member

    I see that, but it's not the absolute flow I am worried about. It is the pressure/flow fluctuations I am experiencing.
     
  15. Harvest Fields

    Harvest Fields Trusted Plumber GSR Top Contributor!!

    Are you saying that for example. Sometimes your bath tap is 8 litres and sometimes it is 15?
     
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