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Gravity shower problems

Discussion in 'Plumbing and Central Heating' started by dormermike, 3 Oct 2019.

  1. dormermike

    dormermike

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    Hello all

    Bit of a difficult one to explain so please bare with me.

    Had a new bathroom fitted a couple of years ago and all fittings replaced. I think they are intended for higher pressure systems but the installer said they were fine for 0.5 bar.

    The problem is that every now and then the shower slows to a dribble. Playing with the hot and cold on the bath and sink will bleed air out and it sputter back to life.

    When it's working properly with decent enough flow the shower flow can be affected by turning the sink hot tap on and off. I.e. shower flow slows briefly when the hot tap is opened. That doesn't seem right to me, as they are fed by separate circuits from the hot water cylinder. But I can't think what could cause it?

    This is a downstairs bathroom in a bungalow with hot water cylinder and cold water feed tank above in the upstairs. No pipework outside the bathroom was changed and it all worked perfectly before the bathroom was redone. Shower is a dual thing with an overhead and a handheld spray. I wondered if it is letting air in when not in use, but that doesn't explain the momentary flow interruption when opening the hot tap.

    Thanks
    DM
     
  2. muggles

    muggles

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    I doubt you have 0.5 bar - that means 5 meters vertical distance between the loft tank and the outlet, which would be difficult to achieve in a bungalow.

    Are you sure everything is fed from separate pipes from the cylinder? That would be unusual, although not impossible.

    It sounds like you're drawing air in from somewhere. Is it just the shower that's affected? Have you checked the float valve in your loft tank is operating correctly, and you're not running it dry?
     
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  4. dormermike

    dormermike

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    Hi sorry I meant that the bathroom fitter told me the fittings were suitable for 0.5 bar. Or at least I think that's the number he mentioned - fine for low pressure systems.

    Yes it's only the shower affected. The shower pipework is a high point though where a previous shower pump was plumbed out. That was all done a long time prior to bathroom being done out and never caused problems.

    You are right too,the hot water tank and cold water tank both have 22mm exits and somewhere under floor boards these turn into 15mm for the shower. The 22mm continues direct to bath for hot and cold (flow not as good as it used to be but no air) with a 15mm T off for hot water to the sink.

    So turning the T'd off sink hot tap makes the shower flow increase and decrease as you turn it on and off. I wonder if there is air making its way into the shower pipework which is compressing when the shunt of water moves with the sink hot tap going on and off?

    The shower is one of these stupid dual head things with a plunger to divert to the overhead one. I wondered if that is leaking and admitting air. Sometimes you hear the shower drain residual water as the bathroom door opens, presumably pressure.

    Stop cock in cold water tank for DHW working fine and is set high enough.

    (Unrelated but the DHW circuit gets a lot of air lately and I have to bleed the boiler side of the circuit - noticed that the central heating feed tank ball cock is not letting in mains cold water - as I say, unrelated just funny how these things get noticed in the run up to winter).
     
  5. dormermike

    dormermike

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    Just bouncing this back up with a question.

    On a gravity hot water system, with two hot taps on at the same time - all things being equal the flow should be the same in both, and opening / closing one of the faucets should not affect the flow from the other - is this correct?


    Thanks
     
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  7. Nozzle

    Nozzle

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    No that is not correct - dynamic pressure is related to flow. As you back off one tap, the flow through the common lengths of pipe slows and so therefore does the dynamic pressure loss. Overall, the pressure available at the still-open TAP increases. It is the same with any system, gravity or pressurised... it's just you might not notice it so much on a pressurised system, as the relative change is less.

    Also, if one tap is at the end of a long length of small dia pipe, it too will see a greater dynamic pressure loss.

    Nozzle
     
  8. DIYnot Local

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