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Discuss Wetroom shower draining slowly in the Bathrooms, Showers and Wetrooms area at

  1. pavsid

    pavsid New Member

    Hi all, I fitted an en-suite wetroom shower a couple of years ago, and for the last 9 months or so it's not been draining too well. I don't remember there being an issue before.

    Initially I thought there could be a blockage so used a solution and an unblocker tool, but that didn't work.

    Then I suspected it could be due to pressure, so I removed the trap from the sink in the en-suite so as to allow air to enter the system freely, which worked very well.

    So I installed an anti-syphon bottle trap (with air admittance valve) on the sink hoping it would fix the issue, but there doesn't seem to be enough vacuum to open the valve. If I open the valve manually then the water in the shower drains away within 20 seconds or so. I can't keep the valve open though because then it leaks when using the sink.

    Is this a common problem? Have I made a school-boy error on the install somewhere?

    I've attached a couple of sketches of what's going on.

    I also recently tried another test - while the shower was running (and filling up) I turned on the basin tap (just enough so that it wouldn't decrease the pressure of the shower too much) - the water collecting in the shower at best stayed the same, if not worsened, and the basin started to fill up. The basin does start to fill up sometimes anyway, but it seemed to fill up quicker today with the shower on.

    Many thanks.


  2. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    How long roughly is the shower waste run?
    Is your soil stack external?
    • Friendly Friendly x 1
  3. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    Also the water does not drain away quicker based on having a higher pressure of water behind it. I’d say your problem will lie with the waste runs or the main soil stack
  4. pavsid

    pavsid New Member

    Hi, probably about 1.5m to the right, then 1.5m out to the back of the house, so around 3m in total.

    Yes the soil stack is external. The basin is attached to an external wall. In the first photo you can see the pipework going out the back of the house. The run to the soil stack (from the basin) must be about 4m.

  5. Pickwickpick

    Pickwickpick Plumber Top Contributor!!

    Sounds like you've got a partial blockage at some point after the sink and the shower waste pipes connect together.

    Have you got a manhole you can lift?
    • Like Like x 1
  6. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    Or your air vent at the top of your stack isn’t working too well
  7. pavsid

    pavsid New Member

    Sorry, when I say I suspected there was a pressure issue, I probably meant a vacuum issue, where the water isn't able to freely run through the pips due to not being enough air in the pipework? I'm no expert, so was just a guess.

    What problem do you think there could be with the waste runs or main soil stack?

    I've attached a photo of the pipework outside, the blue circle is where the shower waste connects. On the far left you can see there is an access plug - on looking through it i can't see any blockages.

  8. pavsid

    pavsid New Member

    I fitted an access plug, and looking through it doesn't seem to be any blockages, on the outside run that leads to the stack at least.

    The stack goes to a sewage pump, so yes I have access to that too.
    Last edited: Jan 16, 2019
  9. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    It’s a long old run outside which still is part of the run.
    Could be poor fall inside?
    Could be that the air vent on the top of your stack is blocked
  10. pavsid

    pavsid New Member

    Hmm, the toilets (there are two leading to the pump) seem to flush fine, in fact I only fitted the vent because they weren't flushing very well - originally i just had a vent stack under the stairs (recommended by building control).
  11. pavsid

    pavsid New Member

    I'm going to have another go at cleaning the internal pipework from the shower. If that fails, all things considered...

    1) Should I increase the fall of the external waste pipe?
    2) Will upgrading the external pipework to 50mm make any difference?

    Any changes to the internal pipework from the shower to outside will require me ripping down ceilings etc, so would prefer to leave that as last resort if at all possible!!
  12. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    I think the fall is okay. But my preference on a run with two appliances running into it would’ve been 50 mm externally.
    • Agree Agree x 1
  13. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    If the toilet work absolutely fine then chances are that it’s a blockage in your smaller pipework
  14. pavsid

    pavsid New Member

    Ok, many thanks. I will try cleaning the pipework first. Then upgrade the external pipework to 50mm. While doing that, I guess I may as well increase the fall a bit just in case. But, how would I cover up the hole where the existing boss strap is on the stack?
  15. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    Is it a black rubber washer in the boss or is it glued in
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