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Discuss Bad smell from around internal soil pipe in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net


I moved house about 9 months ago. Around 3 months after moving in I started to notice an intermittent sewage smell in the bathroom upstairs. For the last few months I have been checking all traps and trying to pinpoint the smell. There is no issue with the traps, I believe the smell is coming out from around the toilet soil pipe connection. This is where there is a gap in between the soil pipe and tiles. You can feel a bit of a draught around the soil pipe and the smell comes with it. Its very intermittent. I have just taken the toilet off but there is hardly any room between the soil pipe and the tiles to take a proper look behind. There are no leaks anywhere in the bathroom or downstairs. Last week I was working in the hallway which is inline to the toilet and I had to lift the floorboards up, as soon as I did that I could smell sewage. Any idea what it could be? Behind the toilet in the box could there be a faulty AAV? There’s only two things I can think of that could be causing the issue - faulty AAV (if there is one) or lose connection somewhere?

Because there is a high box behind the toilet I am taking a guess there might be an AAV in there:


The soil stack is a strange setup. It goes from upstairs then to the downstairs toilet then there is a horizontal run before it drops below floor level with a rodding point. I believe these houses might have originally had a downstairs bathroom only (1950s / 1960s house)


This is the downstairs rodding point – there are no smells around here. If I take the rodding point cap off there is the same smell but nothing is backing up.


The stack terminates outside here with an AAV


I can’t get to the manhole cover – its been decked over(!) there is one 4m before that one though and I have checked and its not backing up / overflowing.

Any ideas? I have just fitted a new flexible pan connector in the off chance its that but it isn't. I think my next job now is to look into the box behind the toilet.


Gas Engineer
Yes I’d be looking for another aav, or perhaps even check the outside one isn’t frozen/stuck.

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