Occasional Sewage Smell Downstairs - Tried Various Fixes with No Success, Need Advice

[bm58xsc8]

Hi all,

My girlfriend and I are plagued by a sporadic smell of sewage in our house, particularly on the ground floor. We've tried several fixes:

1. Testing the Water in Traps: Checked for water in the traps beneath the sinks; all were normal.
2. Air Admittance Valve: Installed one, but no change.

There's no obvious pattern:

• Rain Connection: I thought it might be linked to rain.
• Dishwasher Connection: She believed it was related to using the dishwasher.
• Specific Time in Evening: We even thought it was consistent to a particular time, but this hasn’t held up.

We're also at odds over the source:

• Beneath the Kitchen Sink: Her theory.
• Anywhere on the Ground Floor: My theory.

The water company did inspect our drains but only via a manhole cover in the front garden, ignoring the internal plumbing altogether. They found nothing, and honestly, I don’t fully trust their assessment.

Considering a giant fatberg found a mile from here, we thought something similar might be happening, but our neighbours haven't noticed any smell.

Our next step is to hire a camera to inspect the internal pipes ourselves. We're truly at a loss, and any insights or similar experiences would be greatly appreciated.

Many thanks in advance

 

[oldbutnotdead]

Your central heating boiler- where does the condensate pipe go? They tend to be untrapped, if it is tapped into the soil stack it is a possible odour source.
How sporadic are you talking- once or twice a day?
Are you on a shared drain (do your drains connect to the neighbouring houses or go straight to the street sewer)? Is there an interceptor trap in the manhole that leads to the sewer- if yes, is there a cap on the bypass?

 

[bm58xsc8]

Thanks for your reply

Your central heating boiler- where does the condensate pipe go? They tend to be untrapped, if it is tapped into the soil stack it is a possible odour source.

Not sure about this. The boiler is in the middle of the house. The only large pipe coming from the boiler goes straight to the roof. I actually tried to locate the soil stack but couldn't see anything. I've attached a zip file containing a video of the loft space. I don't know much about this (obvs), but I expected to see something that looks like a soil stack, but nothing.

How sporadic are you talking- once or twice a day?

On average I'd say 5 times a week. Not every day, sometimes twice a day.

Are you on a shared drain (do your drains connect to the neighbouring houses or go straight to the street sewer)? Is there an interceptor trap in the manhole that leads to the sewer- if yes, is there a cap on the bypass?

Absolutely no idea with this. Is there any way for us to check by looking?

 

[oldbutnotdead]

That'll be the flue. If the boiler is aged it won't have a condensate pipe- you need to look for a 30 or 40 mm pipe, usually plastic, going downhill from the boiler.
For the rest, lift that manhole cover and see what pipes are in there and what directions they are going in. Check where your waste is going by chucking a bucket of water down each gulley, sink, shower etc and see where it appears. Also compare how long the flow lasts from each tested item- they should all be pretty similar, if one drain flows for half the time that the others flow it indicates a leak.

 

[Mr Chibs]

Check the seal in the AAV (if possible) I changed one, that didn't seal properly.

Is the AAV downstairs?

If you had the smell before this was fitted then, likely something else. Check soil stack is not vented into shower extractor... if you search on here, you'll see this has happened for others.