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Venting soil pipe

Discussion in 'Plumbing and Central Heating' started by henry1, 3 Jan 2021.

  1. henry1

    henry1

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    Hi,
    I've got a soil pipe terminating just under my upstairs bathroom window. There's an AAV on top. Since it's been installed 2 years ago, it has been working fine until 10 days ago.

    I noticed the water in the toilet would rise excessively when flushing. I first thought it was a blockage but when I removed the AAV, the water level didn't rise. So I changed AAV today to a McAlpine one but the issue remains.

    My understanding is that there is no place for air to escape when water enters the soil pipe via a flush. An AAV allows air in not out, to avoid the bad smells.

    So how was the toilet system working correctly all this time? How was air escaping?
    How do I fix it? A normal soil pipe terminal would allow bad smell out and into the house, being so close to the window... I could continue the soil pipe so it goes through the roof and terminates above it but it will then run in front of the window. I'll still be able to open it but it will look very odd. I can't move it sideways as it is in an internal corner and the window is wide.
     
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  3. CBW

    CBW

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    I’d be looking at a blockage if your new one still has the same affect. Check the manholes first.
     
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  4. henry1

    henry1

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    The water level doesn't rise without an AAV in place.
    Isn't the issue with air flow/pressure rather than blockage?
     
  5. CBW

    CBW

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    Not always. Try what I said, and report back, I’ve had it a few times before, and it was blockages.
     
    Last edited: 3 Jan 2021
  6. henry1

    henry1

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    I initially thought it was a blockage and tried a few easy methods to unblock but they all targeted a blockage just after the toilet.
    Ok, will lift manhole cover and have a peep.
     
  7. Hugh Jaleak

    Hugh Jaleak

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    An AAV lets air in not out. Under normal circumstances this is fine, and it will do what it needs to do. If the stack fills with the outflow from the WC, it will pull some air in behind it, the AAV will open to allow this to happen, and the air in front will be pushed downstream into the drainage system, to be ventilated elsewhere.

    However, if you have a blockage, both ends of the pipework are effectively sealed, so when you flush the WC, the water from the WC needs to displace the equivalent volume of air, which it cannot now do, so the level in the pan rises. If you remove the AAV, the air can easily be displaced out the now open top of the pipe, hence why the level in the WC no longer rises until you replace the AAV.

    My money is on you have a blockage somewhere. Chemicals etc are a waste of time and in fact are dangerous. The only solution to clear that is mechanical means, e.g. drains rods or high pressure water jetting.
     
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  8. henry1

    henry1

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    Good explanation but if I had a normal pipe terminal and no AAV, this would never have been detected.
    I'll look for that blockage...
     
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  9. CBW

    CBW

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    Probably would just have took longer to appear
     
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  11. Hugh Jaleak

    Hugh Jaleak

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    As above. It would either have taken longer to appear, (usually when a manhole or gulley starts overflowing), or sometimes, sheer volume of waste behind the blockage can cause it to shift and the system unblocks itself.
     
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  12. henry1

    henry1

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    Looks like the blockage is downstream?
     

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  13. CBW

    CBW

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    Hard to say from just one manhole, could be blocked further down, or just at yours. If you’re able to check further down, I’d recommend it. Also if shared (not 100% with you being in Scotland) then the water undertaker can unblock it for free.
     
  14. HERTS P&D

    HERTS P&D

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    Get it jetted!

    Andy
     
  15. henry1

    henry1

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    Yes, if anyone does it, it won't be me!
    I think it's shared as it is downstream from me, so I will get in touch with the water company.
    The only concern I have is that I am the first house in the block of terraced house, so my connection to the next manhole is not shared with anyone.
     
  16. HERTS P&D

    HERTS P&D

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    :ROFLMAO::ROFLMAO::ROFLMAO::ROFLMAO::ROFLMAO::ROFLMAO::ROFLMAO::ROFLMAO::ROFLMAO: That's what I do for a living!

    Andy
     
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  17. henry1

    henry1

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    Just an update to say it's been unblocked by the water company.
    It turns out the blockage was 2 properties down the road.
    The neighbours must be shielding so much I haven't seen them at all and they haven't noticed it, probably because they have a fully vented pipe.
     
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