smelly smells from downstairs loo

[Ted808]

hi there... basically went to a cust's house today and it's an upstairs downstairs little terraced house.
Recently the wc under the stairs has been smelly- very smelly at times, mostly in the morning.
It's the usual little room with a basin and hidden pipework- needless to say no visual signs of leaking, but definitely a smell. Above there's another bathroom and the loo (presumably the bath and basin as well ) connects to the same stack. Unfortunately upstairs has a concealed, and well tiled boxed in loo/ cistern. Soil stack doesn't go all the way into the loft, stops here.

So now my question is, IF there's a aav in this boxing would the smells drift down to the loo below?
Does sewer gas rise or fall or does it just seep out where it can?

I've got cust monitoring trap depth and next step - maybe destroy some tiling to check if aav present and failed.... any other suggestions appreciated.

Thank in advance

• :clap:
  

 

[joni os]

Monitoring trap seems the way to go. Remind customer, even with plug in and basin full of water
a failed trap will still allow smell to pass via overflow.

 

[chris watkins]

Rise, as the sewers are all vented an points along the street to stop the build up of methane etc.