Weird intermittent smell in bathroom

[Zimboni]

Hi all,

We have a downstairs bathroom which since we moved in 6 months ago, has an intermittent methane/sewer smell. The toilet is not connected to the main soil pipe, as this toilet was installed at the back of the house after the upstairs one. The waste pipe is in the room behind, boxed in, using an air admittance valve. See attached - I changed the AAV and that seemed to solve the problem. But it seems every Sunday morning we wake up and the horrible smell is back. Not as bad as it was before I replaced the AAV and the smell only seems to last a few hours. I’ve had a plumber check the pipes and they’re all clean - no blockages. The basin and shower have water in their traps and we use them regularly. I’m at a loss as to what is causing this smell to return for several hours every Sunday. We do nothing different at the weekend. Does the AAV look ok? Is it too short? Could the AAV be picking up smells from the neighbour’s (semi detached) waste pipes somehow (if they’re doing something odd on Sunday morning)?

Thanks!

 

[foxhole]

would need pics

 

[Zimboni]

Weird - I did upload a pic, but it never showed up. Hopefully this worked.

 

[Madrab]

Did your plumber not point out that setup isn't correct? Any AAV attached to the stack should at least be above the highest spillover point of the outlets attached to it. In all honesty though, given it's outside that stack it should really be up and over the roof point and be left as an open vent.

Is your drain/sewer open vented somewhere else on that run?

 

[Zimboni]

Is it not above the highest spillover? It is a little bit above the soil pipe (coming from toilet). It was about 10cm higher when we moved in, but he had to cut the broken AAV off and attached the current one.

The former owners did not push it through the roof as it’s in the conservatory. Don’t ask me why that made a difference as I don’t know.

I don’t believe there is any other vent on that run. It runs into the manhole cover about 10 feet away outside. The main soil stack (which is above roof level) also runs into the manhole, but through a different pipe.

 

[denso13]

Is it not above the highest spillover?

That would normally be the top of the wash hand basin and located internally. Although some AAV's do allow a lower external connection.

 

[Nige F]

Hi all,
Could the AAV be picking up smells from the neighbour’s (semi detached) waste pipes somehow (if they’re doing something odd on Sunday morning)?

Thanks!

Nothing odd about a Saturday night curry

 

[Zimboni]

I've contacted the plumber. Told him to rip the whole thing out and put a new one in which is at least 30cm above the handbasin. He's coming out on Wednesday to do it. Thanks for the advice, guys.

 

[Madrab]

The reason I was asking whether the soil run was open vented anywhere else is, if there was a restriction further down, then any pressure created in the soil pipe could leak out from a dry gap joint/seal somewhere, that or water seals could be compromised. An AAV only lets air in to avoid seals/traps from being vacuum'd/pulled if there's positive pressure then it has no where to go so blows back through the pipework.
A soil pipe run should be able to have both positive and negative pressure venting.

 

[Zimboni]

A soil pipe run should be able to have both positive and negative pressure venting.

No other vent I’m aware of. Not sure there’d be anywhere for it to be placed. What would it look like?

 

[Madrab]

an open vent pipe would look just like your pic but instead of the pipe having an AAV on it, it would have a pipe running up above roof point and vent to the air.

 

[denso13]

The main soil stack (which is above roof level) also runs into the manhole, but through a different pipe.

The AAV is ok on that drainage run and is also ok at the height it is at if it is a class 1 AAV. Changing it would rule out/in any issues with it though.

 

[Madrab]

The main soil stack (which is above roof level) also runs into the manhole, but through a different pipe

Apologies, totally missed that comment

 

[Zimboni]

The AAV is ok on that drainage run and is also ok at the height it is at if it is a class 1 AAV. Changing it would rule out/in any issues with it though.

This is the valve that is attached to the stack in the box - it replaced the old one which had failed and had to be cut off - the FloPlast AF110G:

https://www.screwfix.com/p/floplast-af110g-push-fit-air-admittance-valve-grey/78150

So are you saying it’s fine to have this valve only 8cm above the toilet soil pipe?

 

[denso13]

So are you saying it’s fine to have this valve only 8cm above the toilet soil pipe?

I think the minimum should be 200mm above any wet pipe entry so 80mm is a bit low. Nothing I would be worried about though.