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Fast flow shower trap - weird draining problem

Discussion in 'Plumbing and Central Heating' started by tmhs, 10 Sep 2020.

  1. tmhs

    tmhs

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    Location:
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    We've had a shower installed as part of a loft conversion. The problem is that the water doesn't drain out of the fast flow trap quickly enough.

    Behaviour is as follows:
    • Turn shower on
    • Waste doesn't drain, shower tray fills
    • Take out waste, bubbles/gurgling noise
    • Water drains ok
    • Put waste back in when water flowing
    • Waste works as expected - water drains fine
    • Turn off shower and water drains
    • Gurgling noise from waste
    • Turn shower on and waste doesn't drain again, shower tray fills again

    Video of behaviour:



    The run to the vented stack pipe is 40mm diameter with a gradient of 25 mm per meter.

    Sounds like there is a high point causing an air lock when the trap is installed? I'm unsure of the mechanics of it and why it blocks when the trap is installed. Without the trap, water drains with no problem.

    Builder is confused by it and I'd like another opinion.

    We've got a WC basin connected downstream of the shower trap and we undo the bottle trap to allow air to vent. It didn't make any difference to the drainage from the shower trap.

    The trap type allows water through a cylinder section into a 'mini bucket' which overflows into trap and water exists via waste pipe. No hair or dirt in it.

    Suggestions so far has been to cut off 15mm of the cylinder section from the fast flow trap. Did that, no impact.

    Any ideas for further investigation or potential fix?
     
    Last edited: 10 Sep 2020
  2. sircerebus666

    sircerebus666

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    Normally when shower trays fill up it means you might have a blockage downstream somewhere , does the basin drain ok?

    I'm assuming you no longer have access to the waste?
     
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  4. tmhs

    tmhs

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    Yes, the basin does drain ok and shower also drains fine without the waste trap. In actual fact, they both drain fine at the same time. It's just with the waste trap screwed in when we get the problem.
     
  5. Nige F

    Nige F

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    Does the waste from shower go to a 110mm soil pipe .......with a durgo ( air admittance valve ) on it ? or does the svp go to open air (through the roof)
     
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  7. tmhs

    tmhs

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    Yeah - waste goes into 110mm open air soil pipe.
     
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