Smell after flushing toilet

[Brendan]

I have completed 2nd fix plumbing but now noticed there is a smell (soapy poo, like the smell from the local sewage treatment facility) in my downstairs wc/shower room. It is the same smell that came out of the waste pipes before they were connected up. 
 

The smell is very mild unless the toilet is flushed, thereafter it is a lot stronger. I have checked that all the traps (wc, shower, basin) contain water. There are no wet patches or other obvious signs of leaking waste pipes. 

The WC waste turns 90 degrees at the back of the toilet into a boxed-in section which contains an AAV. The easiest place for any smells to emerge from this cavity is behind the WC, which is where the smell is strongest. 

 

The boxed in section is tiled and would be very disruptive to remove, so I wouldn’t want to do this unless I was certain the AAV was stuck/faulty. 
 

Is there another likely cause of this smell and any easy things I can check first?

 

I thought about buying a cheap gas detector, would this be any use?

[ProDave]

What work exactly have you done?  Is this a completely new shower room, or have you just changed the WC in an existing shower room?  

 

At what point did the smell start?

 

Pictures please.

[Russell griffiths]

The AAV needs to be accessible, I believe it’s a building regs thing. 

They do fail so this would be the first point I would look. 

[ToughButterCup]

33 minutes ago, Brendan said:

...
The WC waste turns 90 degrees at the back of the toilet into a boxed-in section which contains an AAV.

...

 

Thats the first place to start.

• Drill
• Hole
• Cheap glass fiber inspection system ( phone + cheap cable)
• Poke
• Look
• Wince.
• Plan
• Repair.

 

[Brendan]

1 hour ago, Russell griffiths said:

The AAV needs to be accessible, I believe it’s a building regs thing. 

 

 Can you (or anyone else) tell me where to find this bit of the regs?

 

I will happily get the builders (with whom I have now parted company for various reasons) to come back and sort it out at their expense and to my satisfaction if this is a mandatory requirement. 

[Brendan]

1 hour ago, ProDave said:

What work exactly have you done?  Is this a completely new shower room, or have you just changed the WC in an existing shower room?  

 

At what point did the smell start?

 

Pictures please.

It is a completely new bathroom in a supposedly Enerphit standard retro fit renovation and extension. All of the bathrooms are in the new timber frame extension. 
 

The photo shows what is now behind the boxed in section. 

[ProDave]

With new work like this, you are supposed to pressure test the pipework before boxing it in, to ensure all the joints have mated properly, none of the seals have been damaged and it is all air tight.  Did the builders do that?  Depending where you are, your building control might want to witness that drain pressure test (they do here).  Without that test done, there are so many places it could be leaking.

[Brendan]

50 minutes ago, ProDave said:

With new work like this, you are supposed to pressure test the pipework before boxing it in, to ensure all the joints have mated properly, none of the seals have been damaged and it is all air tight.  Did the builders do that?  Depending where you are, your building control might want to witness that drain pressure test (they do here).  Without that test done, there are so many places it could be leaking.

No idea. I’m sure they would say they did all of this, and they might have done. They wouldn’t have any proof, I imagine. When I asked what preparation they had made in the stud walls for wall-hung basin/vanity units, they said they couldn’t remember. So I now have floor-standing units instead. 
 

The plumber was one of the main reasons we parted company, mainly because it became evident that the ASHP system had not been designed before installation and wasn’t correctly specified in several respects. They are probably technically competent at plumbing but I would have to learn all about plumbing to be certain (in the same way that I had to learn about central heating and ASHP system design to understand how badly they had approached this aspect of the work). 

[Square Feet]

When I have had this issue in the past it has been because the flexi pipe from the WC wasn't the correct diameter for the soil pipe and there was a tiny gap that the smell came back through.  Even if it is the right diameter I think this is fairly common with flexi pipe as you can't always see what is happening once you shove the pan back into place.