Air Admittance Valve Foul Smell

[markjg123]

Following a home extension, an external bathroom became an internal bathroom and the building regs required the installation of an internal soil stack fitted with an air admittance valve. There's a constant foul smell from the cupboard next to the bathroom, in which the soil stack is housed. Most of the time it's a mild odour, that I can only describe as rotting veg, but this can get significantly stronger, though I don't know what triggers the variation. The soil stack has recently been boxed in but this hasn't made the smell go away. If anything it's generally a bit worse. I'd appreciate any thoughts on what's causing the smell and advice on how to eliminate it.

There was an additional bathroom built above the extension and again the building regs required a soil stack to be installed. This one was sited in the eaves space using the same AAV, a FloPlast AV110. There's never been any odour from that one.

I'm in Scotland in case you're wondering about the building regs requirements.

 

[Newboy]

It's possible the AAV has stuck open or incorrectly fitted

 

[ScottishGasMan]

I'm in Scotland in case you're wondering about the building regs requirements.

Building regs!! never heard that used up here lol. Thought we just did out own thing.

The toilet above the one you have problems with, are they using the same soil stack? Can or is the stack be vented out the roof to outside?

 

[markjg123]

Nope. Different stacks. The upstairs one could be vented to the outside but isn't an issue. The one that is causing a problem can't be externally vented.

Withe regard to incorrect fitting, I'm not sure how it could be. It basically just fits over the soil pipe.

 

[Newboy]

Nope. Different stacks. The upstairs one could be vented to the outside but isn't an issue. The one that is causing a problem can't be externally vented.

Withe regard to incorrect fitting, I'm not sure how it could be. It basically just fits over the soil pipe.

Dependant on brand

some have male fitting with rubber gasket and fit inside the stack
some have female fitting with internal gasket and fit over the stack
some are solvent weld and are glued to the stack

If yours can be lifted off without any difficulty then it may be missing a seal or should be solvent welded to the stack.

EDIT - I've just seen the model number in your first post - it is a solvent welded version. Can you remove your AAV by lifting it of the sub-stack? If so then it has been installed incorrectly and should be solvent welded to the stack pipe. Before you weld it I would check that it is operating correctly.


Even a very small air gap will allow significant quantities of foul gas to escape every time the stack is used

 

[Newboy]

Sorry - I forget to ask you a basic question.

How high above floor level is the top of the AAV in question?

 

[markjg123]

Thanks newboy. I can easily remove the AAV from the stack. If try to unscrew the top off it then the whole AAV comes off the pipe. It hasn't been solvent welded

The top of the AAV is approximately 750mm above floor level.

How do I check it's working correctly? I've removed the AAV and it looks pretty basic in design.

One thing I have noticed though is that there is absolutely no bad smell coming from the pipe in the attic space. The smell from the downstairs cupboard pipe is really pungent. Is this normal with soil stacks?

 

[Newboy]

Take it off the stack and invert it repeatedly - you should hear the flap opening and closing.

If it works then get a pot of solvent weld and fix it in place or, a better solution, replace it with a gasket version. This means that, should access to the stack be required at some point in the future, it can be removed.

 

[markjg123]

I think I'll just replace it. It's only a few quid from Screwfix if this is the right one.

http://www.screwfix.com/p/floplast-...10/78150#product_additional_details_container

Thanks for all you help. I'll let you know how it works out.

 

[Newboy]

Just a quick point.

Technically your AAV is too low - it should be 300 mm higher than the overspill level of any appliance connected to it. If there is a basin in the bathroom then this is usually the highest level - so 300 mm higher than the basin rim is the specified level.

 

[markjg123]

Does this affect the performance of the AAV or merely increase the risk of an overflow in the case of a flood? I could replace the stack and I'd have to rebuild the box too.

 

[Newboy]

In practical terms I wouldn't worry about it

 

[markjg123]

OK thanks again. I'm off to get the new AAV and hopefully that will sort out this problem. I did also notice that the soil pipe isn't cut perfectly square at the top. Is that a problem?

 

[Newboy]

not usually a problem - just make sure that the gasket doesn't snag when fitting the new AAV

 

[markjg123]

Will do. Thanks.