Faulty soil pipe air admittance valve? Need some help

[Stonedofmoo]

Hi guys

I'm hoping you can help me as I'm no plumber! I live in a townhouse that's about 5 years old, we moved in last summer. Since pretty much day one we noticed the shower and toilets drain slowly. In our ensuite bathroom the toilet pan can sometimes fill close to the top when flushing before draining, and when it does the waste on our shower bubbles and burps suggesting an airlock.

Similarly if we have a shower upstairs the toilet in the middle bathroom bubbles through the waste in the pan, so clearly we have pressure problems somewhere.

I was up in the loft and noticed the soil pipe which in these new houses seems to be inside. I noticed it has a cap on top which research tells me is an air admittance valve.

To experiment I tried removing the cap so the pipe is open, and voilá! immediately all the drainage problems go away. Screw the cap back on and they return.

Is this valve likely to be the problem? I don't see any moving parts and I can't really see HOW it's the problem, but there is no denying unscrewing the cap stops the issues in the house.

I've taken pics. The valve appears to be a Center air admittance valve 110mm which unfortunately also seems to have been solvent welded onto the waste pipe.

What should I do? I can buy a new one but I can't remove the part that's welded on and I don't really understand how it could have failed?

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• Stonedofmoo
• 4 Jan 2015
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• Stonedofmoo
• 4 Jan 2015
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• Stonedofmoo
• 4 Jan 2015
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• Stonedofmoo
• 4 Jan 2015
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• Stonedofmoo
• 4 Jan 2015
• 1

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• Stonedofmoo
• 4 Jan 2015
• 1

Any ideas people?

Best regards
Chris

 

[stardanny]

You have a blocked drain somewhere. Have you got manholes? Lift and check if empty or full of water.

The air admittance valve only let air in and stop drain smell coming out.

Daniel.

 

[denso13]

Sounds like it's sticking closed somehow. I'd be tempted to fit a new one if you can't vent it to the outside.

 

[Stonedofmoo]

You have a blocked drain somewhere. Have you got manholes? Lift and check if empty or full of water.
Daniel.

Hi there. Good thought, I went outside and lifted the drain cover. All looks well..

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• Stonedofmoo
• 4 Jan 2015
• 1

Denso. I'd be happy to fit a new one, but certainly one piece of it is soldered onto the waste pipe so I can't remove that. Also what part exactly would be sticking closed. I expected to see springs or something inside it, but there isn't anything except what you can see in my pictures

 

[denso13]

Dunno what is sticking exactly but if it all works ok with the cap off there is something wrong with it. Yours is a Center Brand (Plumb Center) but they work like this http://www.polypipe.com/cms/toolbox/Air_Admittance_Valve_Installation.pdf

 

[stardanny]

Can you confirm the drain is coming from toilet and soil stack?
Leave the manhole cover off and flush toilet. If it still causing problem, there is a blockage between manhole and the base of soil stack. If it cured the problem with manhole cover off, there must be a problem further down stream.

Daniel.

 

[denso13]

The problem goes away with the cap taken off the AAV. You sure it's a blockage?

 

[Stonedofmoo]

Hi Daniel

Sorry but I don't understand this. Can you explain the logic, why you think it's the drains that's the issue?

Surely if they were blocked or running slow it would make no difference if the admittance valve cap was on or off but yet the issue goes away when the cap is off. Also why would drains cause the wastes to run slowly 2 floors up in a town house?

Regards
Chris

 

[stardanny]

The problem goes away with the cap taken off the AAV. You sure it's a blockage?

AAV only let in fresh air, and stop drain smell coming out.

As the toilet is flushed, water has to go into drain, if there is a blockage in drain, water will build up, forcing air out and as AAV is shut on positive pressure, the only way for air to get out is thru shower trap.

Daniel.

 

[denso13]

Hi there. Good thought, I went outside and lifted the drain cover. All looks well.

If you flush the toilet with the AAV cap off does the water come through the manhole ok?

 

[Newboy]

Agree with stardanny 100%

The removal of the AAV is allowing positive pressure to vent - to prove the point put a bin liner tightly over the open pipe and see if it moves up when you flush the pan.

Classic blocked/obstructed drain behaviour - I've seen dozens where the AAV is removed and the problem seems to go away until the drain backs up completely

 

[yebaws]

AAV are notoriously unreliable. Can you hear the air coming in when a toilet is flushed? Why not just replace it and see (they're not expensive). If everything works with the AAV off then it would also work if you had an open vent on the roof. And your drains are clear from your pic.

 

[Stonedofmoo]

Yep stardanny you know your stuff!

OK so we have 3 toilets in our house. The hatch I lifted earlier only appears to feed the downstairs toilet, and that's never shown a problem. We realised there was another drain cover when we did the upstairs loo and no water came through

When I lifted the cover for the second hatch it was a different story straight away. Already there was water pooled inside and it looked 'dirty'
I got my wife to flush the upstairs toilet and the water came down slowly, plus there was a gurgling noise outside. The water level immediately started to build up inside the hatch area rather than flow through the pipes into the street, and it took around a minute to return to it's lower level.

The water is moving but it's very sluggish. It seems the block is somewhere between the area I can see in the hatch, and the main pipe in the street.

The hatch isn't very large. I don't think traditional drain rods could be pushed into the pipe. Does anyone have any recommendations for a drain rod kit for 'modern' drains as I'll need a very flexible pipe to bend it into the drain and try and plunge the pipe to remove the block.

Cheers guys

 

[stardanny]

If the second manhole is the same as on photo you shown, any drain rod set will get in there, I've used my rods before on same type of manhole.

Or call out for drain jetting service.

Daniel.

 

[uknokianut]

Did you ever resolve this as I've got a similar problem with a Center air admittance valve ?

And does the rubber part face up or down ?