Anyone have any idea why when I flush my toilet, my utility room stinks of sewage. This  only happens for a few mins and then the smell disappears again. 
I have a washing machine in there and a boxed in soil pipe that’s unused was supposed to be for an ensuite. 
could the  washing machine trap be getting sucked out? 
when I check the trap it’s got water in it though. 

Check the unused boxed in soil pipe, is it properly capped possibly with an AAV?

I had this happen this week... Turns out to be the main waste line to the public sewer is blocked. So when you flush, there is a pocket of pressurised air in front of the water that will need to escape. That usually means any trap between the blockage and the flushed water. 

I’lll have a look tonight the pipe extends half way up the bedroom above it. Could the AAv opening cause the smell? 

1 minute ago, Conor said:

I had this happen this week... Turns out to be the main waste line to the public sewer is blocked. So when you flush, there is a pocket of pressurised air in front of the water that will need to escape. That usually means any trap between the blockage and the flushed water. 

Is it possible for the trap to be sucked out and then reappear without be running water through it? Silly question I know 

5 hours ago, Conor said:

I had this happen this week... Turns out to be the main waste line to the public sewer is blocked. So when you flush, there is a pocket of pressurised air in front of the water that will need to escape. That usually means any trap between the blockage and the flushed water. 

 

+1 it explains why there is still water in the trap.

 

I would have a listen in the utility room while someone flushes the WC to see if you can hear it gurgle/bubble.

Had a listen there nothing obvious. I can hear the sink drain from the bathroom. So that must connect to the washing machine drain. 
it’s weird that the smell goes away after a few mins.
I checked the unused soil stack it’s capped off has no Aav. 

Where is the toilet? Ground floor or first? 

1 hour ago, Nickfromwales said:

Where is the toilet? Ground floor or first? 

It’s on the ground floor Nick 

Has someone stood in the utility whilst the WC is flushed to listen for pipes ‘burping’ out stench from the foul system?

5 hours ago, Nickfromwales said:

Has someone stood in the utility whilst the WC is flushed to listen for pipes ‘burping’ out stench from the foul system?

I have listened for noises but nothing obvious. I’ll check again tonight and give it a good smell when the toilet had been flushed.

This waste pipe in runs out to a trapped gully. I don’t know if that makes a difference

 

Edited November 25, 20223 yr by Alwayslearning22

On 25/11/2022 at 08:19, Nickfromwales said:

Has someone stood in the utility whilst the WC is flushed to listen for pipes ‘burping’ out stench from the foul system?

There’s no smells coming from the pipe either 

Why not post some pictures of the pipework and what connects where, it might give someone a clue.

Heres a plumbing layout if thats any use to you guys?

It is symptomatic of a failed AAV. What does the stack do after it rises from the ground floor > bedroom? 

21 hours ago, Nickfromwales said:

It is symptomatic of a failed AAV. What does the stack do after it rises from the ground floor > bedroom? 

It rises to the bedroom and is capped off. I had a look at it last year and it looked like a cap on it. Must be an AAV? Would it be standard practice to put an AAV on an unused stack like that?

Why not block the unused soil stack with a bung in the inspection chamber?

8 hours ago, Mr Punter said:

Why not block the unused soil stack with a bung in the inspection chamber?

Never thought of That to be honest. Could do that. Although I’m thinking is the unused one venting my system. Would it have a negative effect?