bathrooms smell bad, despite AAV fitted

[redhexagonal]

I have a bathroom above a shower room, sharing a soil stack. When I moved in there was a bad smell in the attic and black mould above the soil stack which was venting open into the attic. This didn't seem right so I fitted an AAV in the top. However, since then there is a bad smell in both bathrooms. I've noticed gurglinging sounds in the p traps of the bath when I flush the loo, and I tried putting the plug in which stopped the smells in that bathroom.There are all kinds of weird gurgling sounds when I use the sink upstairs. But the ground floor shower room, I'm not sure, maybe its coming from the sink. I think the AAV isn't letting air in fast enough and the p traps are emptying in the sinks and bath which lets sewage gas in. My house is the highest of a block of four that were built in a terrace on a slight hill. There is a small en suite the other side of the house which has its own soil stack vented through the roof.

How can I stop these bad smells? is the AAV working properly?

 

[HERTS P&D]

First check all your manholes.

Andy

 

[redhexagonal]

First check all your manholes.

Andy

Sorry what am I looking for and why?

 

[Hugh Jaleak]

AAV's do exactly what they say on the tin, they let air in. I would firstly go with Andy's advice above, check any manholes/inspection chambers outside of the property, see if any are blocked.

You have the classic signs of a blockage, basically, as you are discharging an appliance, the volume of water you are putting into the drainage system cannot get away, due to a blockage. Therefore it need to displace the same volume of air from within the pipework, upstream of the blockage. The AAV wont let it out, so it looks for an alternative exit, usually a shower or basin trap. Hence the stink.

 

[freddiemercurystwin]

Hypothetically, he could keep running water from an upstairs basin and it should begin to back drain into a sink or something on the ground floor?

 

[redhexagonal]

AAV's do exactly what they say on the tin, they let air in. I would firstly go with Andy's advice above, check any manholes/inspection chambers outside of the property, see if any are blocked.

You have the classic signs of a blockage, basically, as you are discharging an appliance, the volume of water you are putting into the drainage system cannot get away, due to a blockage. Therefore it need to displace the same volume of air from within the pipework, upstream of the blockage. The AAV wont let it out, so it looks for an alternative exit, usually a shower or basin trap. Hence the stink.

But when I flush the toilet, the water level in the p traps moves down , not up

 

[redhexagonal]

Hypothetically, he could keep running water from an upstairs basin and it should begin to back drain into a sink or something on the ground floor?

That doesn't happen

 

[HERTS P&D]

Sorry what am I looking for and why?

A blockage!

Andy

 

[opps]

But when I flush the toilet, the water level in the p traps moves down , not up

I am not a plumber but I have witnessed the same thing in many customers' homes.

On each occasion it was a partial sewer blockage. For whatever reason the blockage resulted in a vacuum sucking in air through the bath/basin traps.

 

[redhexagonal]

A blockage!

Andy

my first problem is that one manhole at street level out front is partially concreted over, and the second , one floor down from street level , out back is too heavy to lift, its got inset slabs ,and i couldnt get a crowbar under it . And what do i do if there is a blockage?

 

[HERTS P&D]

Looks like this is not a diy job, you will need to call out a drainage engineer to check for you.

Andy

 

[opps]

Thinking about it... the vacuum makes sense... when flushing a loo, ordinarily, the volume of water will not be sufficient to occupy the whole diameter of the soil pipe/sewer, if there is a partial blockage, the "liquid" will force it's way forward and no air will be able to maintain the pressure parity, hence the need to suck air in from elsewhere, in this case u-bends.

Hopefully someone else can explain it more precisely than me . I would however add that I would have expected the top of the soil pipe to admit the air, the fact that it hasn't would lead me to guess that the partial blockage may be in soil pipe before hitting the main vented soil pipe.

....or I may be talking rubbish.

 

[redhexagonal]

Looks like this is not a diy job, you will need to call out a drainage engineer to check for you.

Andy

I’m still thinking maybe the AAV isnt working great because there are no gases in the bathrooms when its taken off, attic stinks though

 

[Hugh Jaleak]

Thinking about it... the vacuum makes sense... when flushing a loo, ordinarily, the volume of water will not be sufficient to occupy the whole diameter of the soil pipe/sewer, if there is a partial blockage, the "liquid" will force it's way forward and no air will be able to maintain the pressure parity, hence the need to suck air in from elsewhere, in this case u-bends.

Hopefully someone else can explain it more precisely than me . I would however add that I would have expected the top of the soil pipe to admit the air, the fact that it hasn't would lead me to guess that the partial blockage may be in soil pipe before hitting the main vented soil pipe.

....or I may be talking rubbish.

Wrong way round. If the pipework is technically 'sealed', by a blockage at the bottom end, the AAV at the top, and the various traps connected to it, the amount of air within the void remains constant. However, when a WC is flushed, then that's 6 litres of water that now needs to displace 6 litres of air. So that air looks for the easiest way out, usually the weakest trap.

I’m still thinking maybe the AAV isnt working great because there are no gases in the bathrooms when its taken off, attic stinks though

Both Andy and I have told you what the issue is likely to be. Removing the AAV will buy you some time, it wont solve the issue.

If you're unable to lift the Manhole covers, then I'd firstly try your Water Company, if the issue is in the street, outside of your premises, then it should be their issue to sort anyway.

 

[redhexagonal]

Wrong way round. If the pipework is technically 'sealed', by a blockage at the bottom end, the AAV at the top, and the various traps connected to it, the amount of air within the void remains constant. However, when a WC is flushed, then that's 6 litres of water that now needs to displace 6 litres of air. So that air looks for the easiest way out, usually the weakest trap.



Both Andy and I have told you what the issue is likely to be. Removing the AAV will buy you some time, it wont solve the issue.

If you're unable to lift the Manhole covers, then I'd firstly try your Water Company, if the issue is in the street, outside of your premises, then it should be their issue to sort anyway.

I’ve bought some manhole keys, will get a mate to help lift it.
I think the sewer goes along the back of 4 houses, and I know the last one (lowest) has had problems with blocked drains. Would I need special equipment to unblock the drain or can I use a hose?