Bad smell in bathroom - coming from Soil Stack?

Hi

I moved into a new 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. 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? I know a bit about plumbing, but this has got me stumped. I am dreading having to chip the tiles off to find the issue. If I got a professional plumber in what would they check that I can’t? Use a camera etc? 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 what I think is 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 ordered a new flexible pan connector in the off chance its that but that wouldn’t explain the smell under the floorboards in the hallway off the bathroom.

Good grief, bodge city there. No Plumber would put their name to that contraption of pipework, and I hope the decking is removable to get to the buried manhole?

Right,, my advice is to firstly, get rid of that external AAV, it's too low down, (AAV's need to be fitted above the spillover level of the highest appliance on the run, in this case the upstairs WC (or basin if there is one). Secondly, I'd hazard a guess there is another AAV behind that boxing in and it's stuck open. Buying a cheap Endoscope might be worthwhile before destroying the bathroom to look.

The system should be vented at some point to atmosphere, do you have another open vent anywhere else on the property? Lastly, avoid flexible pan connectors, no Plumber will use one unless there is absolutely no alternative.

Hugh Jaleak said:

Good grief, bodge city there. No Plumber would put their name to that contraption of pipework, and I hope the decking is removable to get to the buried manhole?

Right,, my advice is to firstly, get rid of that external AAV, it's too low down, (AAV's need to be fitted above the spillover level of the highest appliance on the run, in this case the upstairs WC (or basin if there is one). Secondly, I'd hazard a guess there is another AAV behind that boxing in and it's stuck open. Buying a cheap Endoscope might be worthwhile before destroying the bathroom to look.

The system should be vented at some point to atmosphere, do you have another open vent anywhere else on the property? Lastly, avoid flexible pan connectors, no Plumber will use one unless there is absolutely no alternative.

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Cheers Hugh - what would you replace the AAV with? There is a window right next to it. There isnt an open vent at all so I am thinking of just extending that soil pipe 900mm above the window and having it open? It will be 3m away from the main windows of the house (but still lower down - but i think thats ok looking at the regs).

Also I replaced the flexible pan connector last night (sorry too late ), and it slid into the soil pipe a bit too easy for my liking. I actually think the soil pipe section sticking out is just a branch end - as it has a thicker rim at the end. But it doesn't have a small length of pipe on it - so the flexible pan connector is going straight into the push fit entry - does that make sense?

Ok, if you can remove that external AAV and continue the pipe upwards to vent, that will hopefully help, as long as it doesn't introduce an odour issue elsewhere. Maybe try it and see what happens.

Yes, the finned end of a pan connector is designed to fit tightly into the pipe, not a socket. Advise putting a short section of 110mm pipe into the socket, then the pan connector into that. (Chamfer end of pipe and lubricate the seal before fitting or you'll push the seal out.)