Intermittent bad smell

[Last Plumber]

@Last Plumber the soil vent isn’t something that mapped. How would I check if it’s that?

What does mapped mean?

 

[MatthewG]

What does mapped mean?

Sorry I meant that I haven’t mapped out the network so I’m unsure where the vent is. But when I find it, what’s the deal? How would I know is that’s the problem?

 

[Basher]

MatthewG
When I originally read your first post, I couldn't understand why you were concentrating on the smell coming from your central heating system. My first thought was that it would be from the drains. Maybe coloured by having drain smell problems in our property.
The obvious thing to check is to ensure all traps are full of water (unless you've got Hepvo traps), sinks, basins, showers, any separate vertical wastepipes for washing machine/ dishwasher etc. Particularly looking at any that are infrequently used.

There should be a vent open to atmosphere (outside the building!) somewhere in the drainage system, possibly even in an adjoining property. The reason is to relieve any occasional positive pressure in the system, and without this, smells can find their way by blowing past traps, or through a faulty Air Admittance Valve, or through any leaking joint, into the house. It's become the norm to install AAV's in new bathroom or toilet conversions, but they are only to allow air into the drainage system, to stop a vacuum forming from say a toilet flush, which could suck water out of a trap. So here again, a 'stuck' AAV could result in a trap emptying enough to allow smells into the room.

I bought one of these to track down the source of sewer gas. It can be a bit sensitive to set up/ adjust, but it did work!

 

[John Coen]

Have seen back inlet gully's get blocked and siphon seal from traps.

 

[MatthewG]

I looked for the waste pipes earlier and noticed this. That's the vent right? Surely that should stop there.

 

[ShaunCorbs]

That would do it need extending externally

 

[MatthewG]

Would an air admittance valve work here?

 

[Basher]

Would an air admittance valve work here?

Yes. It would certainly improve matters regarding smell.
I think many would fit an AAV in your situation.
In theory there should be a vent to atmosphere somewhere in the vicinity, so if you, or even your neighbours, have another open soil stack on the outside of the house, I believe an AAV would be in order here.
Is there any evidence that the pipe in your photo used to go through the roof? Another issue to consider is if there are any opening windows above where the pipe would come out.

 

[ShaunCorbs]

If you have another vent to outside then an aav would be fine