Waste smell in bathroom - can’t locate cause

[koopah]

Hi all, looking for some advice if I may. I had a loft conversion 3 years ago including an en suite Bathroom. It’s all been fine until about a week ago when I started to notice a waste smell in there which has been getting worse and worse.

Pretty simple setup, stack running up the corner of the house supporting this and two other bathrooms which are fine. At the highest point, it is vented via a flexible hose to a roof tile vent, I can access this as it’s in the void from the loft conversion, it doesn’t seem to smell at all in that void. The Problem bathroom has waste from a shower, sink and toilet, the smell doesn’t seem to be coming from the sink or shower.

The toilet is fitted flush up against a box which contains the cistern, waste goes from the toilet in to the box then left to the stack via a waste pipe that is boxed in.

It’s when I take the lid off the box containing the cistern where the smell is strongest, it has to be coming from here but all joins look good with no visible gaps and there are no leaks whatsoever.

The vent pipe on the stack in the loft void had come loose, it wasn’t fitted very well at all and there is a lot of airflow in there so I wondered if the smell was travelling through the boxed in waste pipe to the box that the toilet is mounted up against. So I replaced the vent pipe with an air admittance valve on the advice of a local plumber but alas the smell is still there.

I’m at a total loss what to do next, would really appreciate any suggestions!

 

[Ian H]

Try removing the air admittance valve and reinstating the vent, then put a smoke bomb in a manhole outside.

You should see the smoke enter the room where ever the smells are getting in.

 

[aptsys]

Also assuming no joy from the smoke test, it's worth a check for dead vermin. Catches many people out, especially if they have cats.

 

[koopah]

Thanks both.
Im pretty sure it’s not a vermin smell, but will have another look just in case.
Will find where to get a smoke bomb from and locate the manhole outside, fingers crossed.

 

[Ian H]

I usually think dead things smell like a burning clutch.

 

[lostinthelight]

Thanks both.
Im pretty sure it’s not a vermin smell, but will have another look just in case.
Will find where to get a smoke bomb from and locate the manhole outside, fingers crossed.

https://www.screwfix.com/p/arctic-products-smoke-pellets-5g-10-pcs/64647

 

[opps]

I usually think dead things smell like a burning clutch.

I'd say they smell more like the exhaust air from the cooker hoods at a chinese restaurant.

Years ago I made the mistake of filling the entrances to rat nests in a client's foundations after pest control warned the client that they would end up with a fly infestation once the rats die. Bad move. Allowing the rats to decompose naturally over summer took ages. I could smell the pong coming out of the airbricks from 20 metres away.

My next job was near a chinese restaurant, when the wind blew towards me the smell left me gagging.
I am not suggesting that they were cooking rats or anything like that but the smell instantly reminded me of the decomposing rats.

 

[Nige F]

So I replaced the vent pipe with an air admittance valve on the advice of a local plumber but alas the smell is still there.

I’m at a total loss what to do next, would really appreciate any suggestions!

That was bad advice - they have their uses but..................

 

[lostinthelight]

Wouldnt partially blocking the stack at the vent opening so the smoke could build a little pressure be a better option??..