Hot water pressure from a combination cylinder.

Discussion in 'Plumbers' Talk' started by Matty_uk, Mar 26, 2007.

  1. Matty_uk

    Matty_uk New Member

    Hi all. Thought I might pick your brains on this one - must come up at other times, but noone has suggested to me a good solution:

    I live in a one-storey flat with mains fed cold water and hot water from a combination cylinder (the type that has a big hot water tank and a smaller cold water tank immediately above this, the two tanks being built together in the same unit). Hot water is therefore gravity fed from this lower tank.

    Hot water flow in the bath is ok, as it is low down and 22mm piping. Hot water in bathroom sink is ok (just) and is run in 15mm pipe off the 22mm pipe running to the bath.


    The kitchen is the problem - The hot water flow to a small kitchen tap is not good. If I fit a larger (mixer) tap, the flow is pitiful (less head as tap higher).
    Kitchen hot tap is plumbed in 15mm pipework which spurs off the main 22mm pipe which runs from the combination cylinder mentioned to the bathroom. Total length of 15mm pipe from reducing tee to tap is about 3m.


    Question: How can I increase hot water flow to the kitchen tap?

    - Will buying a special low-pressure tap make a big difference?
    -Will reworking in 22mm change much?

    -I'm keen to hear ANY ideas or suggestions you all may have

    NB. The building has no gas.

    Sorry for the essay. Thanks in advance for your help!
    M
     
  2. Captain Leaky

    Captain Leaky New Member

  3. Matty_uk

    Matty_uk New Member

    Hi Captain Leaky. I managed to get hold of Salamander and they said that I can't fit a pump as there is sol little cold water storage. The pump would just run dry in no time at all.

    Thoughts?
     
  4. Captain Leaky

    Captain Leaky New Member

    True if you leave it running for long periods. It will be ok in short bursts such as filling a sink, washing up etc. They are right in that the c/w header on a combi is quite small and wont refill quick enough before the pump empties it and air is sucked in. I have fitted them like this in the past and they work OK. Just make sure if you do it is only boosting the kitchen tap and not the whole house or you will keep sucking in air.
     
  5. Captain Leaky

    Captain Leaky New Member

    By the way, reading your first post again, the problem with the mixer may just be that it is only suitable for high pressure, you need a low pressure mixer tap.
     
  6. if you just wanted to give the hot water a bit of a boost another option is to fit a grundfos UPA 15-90 booster pump to the hot water pipe from the cylinder

    these are a bit different to the salamander as they are based around a central heating type pump so they are almost completley silent

    it will add between 0.5 and 0.75 bar to the hot water pressure

    not as powerfull as the salamander but cheaper, easier to fit (in my opinion) and a lot quieter. worth considering if you only need a bit of extra pressure
     
  7. bathroom boy

    bathroom boy New Member

    Have the mixer been changed recently, if so are they high pressure taps, may be worth trying a new tap which is compatible with a gravity system.
     
  8. problem is guys most of the nice kitchen taps (the ones that her in doors will want) all seem to be high pressure these days

    a lot of the low pressure ones look rubbish
     
  9. Matty_uk

    Matty_uk New Member

    True story about the low pressure mixer taps, plus I suspect it won't make much difference as we're looking at a head of less than a metre in the kitchen.

    Are these pumps one way? ie if I put it in the middle of the pipe section that runs from the 22mm hot water pipe to the kitchen tap, it will only boost the kitchen tap and not the bathroom, and then I don't need to worry about someone running a bath and draining the cold water tank (resulting in the pump pumping air)??

    Would that work? Are there any regs I should worry about here?
     
  10. Captain Leaky

    Captain Leaky New Member

    It's 15mm so fit under the sink ( Salamander ) the other pump is 22mm so yes fit in line.
     
  11. Captain Leaky

    Captain Leaky New Member

    visit the Grundos website for more info, they too are a helpful mob.
     
  12. Matty_uk

    Matty_uk New Member

    Any thoughts on whether replacing the 15mm with 22mm is likely to do me much good?
     
  13. Matty_uk

    Matty_uk New Member

    ...and if I replace with 22mm but have a section where the pipe has to be 15mm, will this temporary reduction in bore completely remove any advantage of having run the pipe in 22?

    Thanks
    M
     
  14. Matty_uk

    Matty_uk New Member

    ok, scratch the 22mm rework idea.

    Captain Leaky, I'm not sure I understand you correctly re. the pump location. This is the system I have:

    http://s68.photobucket.com/albums/i24/mattyuk2006/?action=view&current=Presentation1.jpg

    The pump manufacturers I have spoken to say it should be ok with a low power pump, and they say put it at location A on the diagram above.

    They all said it's better not to put it at B, but I'd rather do that, as it means the bath wont be pumped water. This in turn means that only the kitchen will be pumped, and I think this is less likely to empty the cold water storage/header tank (which would damage the pump) than having the whole flat drawing from the pump.

    Is there a problem with putting the pump at B that noone has mentioned? What would you do?

    Thanks in advance. I know this has dragged a bit...
    Best
    M
     
  15. Captain Leaky

    Captain Leaky New Member

    A low power pump should be OK at A, a higher power pump at B, go with what the manufacturers say and you should be alright.
     
  16. fluxylad

    fluxylad New Member

    if you put the pump in position b,is there a risk that when drawing water in kitchen and somebody draws water in the bathroom,will the pump try to pull through basin or bath tap?
     

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