Kitchen Tap replaced, cold pressure issues

Discussion in 'Plumbers' Talk' started by idrinktea, Nov 12, 2017.

  1. idrinktea

    idrinktea New Member

    I recently replaced my kitchen tap with a low pressure one as my hot water pressure is poor. (Gravity fed, in a ground floor flat)It is great as the hot water pressure has improved. However if I connect turn the cold water (direct from mains) via a check value to the kitchen tap, (cold tap off) cold water is mixing into the hot.

    This is the tap I bought... https://www.screwfix.com/p/deck-mounted-mono-mixer-kitchen-tap-chrome/4505t?_requestid=187537

    I think the cold pressure is too high, adjusting the flow on the check value helps a little but really makes the cold flow poorly, but if I don’t I don’t get any hot water.

    Is either of the following a good idea?

    1. Fit a one way value on the connection to the hot tap to minimise the back flow of cold water?
    2. Fit a pressure reduction value after the check value on the supply to the cold connector (if so what would I need? - really hoping for something cheap and cheerful!)

    Thanks
     
  2. Pollowick

    Pollowick Screwfix Select

    You certainly need a check valve on the hot side - that will stop back flow

    As for a PRV on the cold - it depends on the differential.
     
  3. Hi idt.

    I don't understand this: "However if I connect turn the cold water (direct from mains) via a check value to the kitchen tap, (cold tap off) cold water is mixing into the hot."

    How can the cold mix with the hot if the cold tap is off?

    I'm assuming you mean that when both the hot and cold taps are running, you get the cold pushing the hot back up the hot supply pipe? Can you confirm, please?

    A non-return valve should stop this happening, but it'll also add some resistance to the hot flow and reduce it a bit - tho' I don't know by how much. But, also, if the cold pressure is so high inside the tap that it currently sends the hot back from whence it came, then it'll still be high enough to simply stop the hot flow in its tracks after the non-return valve is fitted. Surely?

    So, I'm guessing the 'solution' is a tap with a split flow right to the nozzle tip, so there's no risk of the cold affecting the hot. Or else a PRV on the cold to knock its pressure down to well under 1 bar, and this shouldn't - in theory - affect the flow that much.

    By turning down the isolator valve, you are affecting the flow and not the pressure (although the two are connected), so to get the pressure down to the point where it isn't affecting the hot, you have also reduced the flow down to an unacceptable level.

    PRVs, on the other hand, are clever and control the pressure but in most cases the flow is unaffected (unless you tried running two taps from one valve, etc).

    So, find out if that tap 'mixes' the water inside its body before it exists the nozzle and, if so, replace it for one that doesn't. Or else, I guess, fir a PRV on the cold and knock it right down...
     
  4. The Teach

    The Teach Screwfix Select

    Another kitchen mixer tap problem, not been one for a few days ;)

    The taps are advertised as suitable for low & high pressure but they for some reason never mention the supplied hot&cold water flow/pressure at the tap inlet has to be balanced or very nearly balanced.

    Mains water and gravity loft tank water are as far from balanced as it gets,

    Fitting of non return valves,pressure reducing valves can help back flow but can create other problems. Its also more expense,

    As DA has mentioned suitable taps are available for UK kitchen sink mains/gravity but there is little choice and usually not as fancy.They have dual spouts and dual tap body so the hot & cold only comes together when exiting the spout.
    Look for the words 'cool touch spout' or 'dual spout' or 'dual flow' But always check as some sellers get their advertising wrong.

    .http://www.bristan.com/products/kitchen-taps

    iirc their 'club budget sink mixer' is a dual flow.
     

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