Why an Air Admittance Valve is not working

[Paul Cockhill]

Hello Everyone

Thanks for previous advice on an Air Admittance Valve height. I have fitted the AAV, see picture, but each time I flush the WC the WC pan fills up to over 80% capacity before it slowly empties. I dont think the AAV is working well enough??, because if I lift the valve slightly the WC empties as normal.

Is it a question of getting a better AAV? or is there something wrong with the pipework? I have a washbasin waste with an anti syphon connector and a bath with a HepVO on the pipe and they empty without a problem

What make of AAV would people recommend?

Thanks

Paul

 

[Chuck]

Air admittance valves only fix issues arising from negative pressure in the drain. If you have a downstream blockage you'll get positive pressure and the symptoms you describe.

Lift the nearest inspection cover and see whether that restores normal flushing and also that the flushed water comes past nice and briskly rather than as a trickle. If so, your problem probably lies downstream. If not, it's between the loo and the inspection cover. Divide and conquer.

[BTW, I don't really do drains but I don't like internal AAVs much and yours looks a bit low to me. Have you checked the manufacturer's installation instructions?]

 

[Harvest Fields]

Air admittance valves only fix issues arising from negative pressure in the drain. If you have a downstream blockage you'll get positive pressure and the symptoms you describe.

Lift the nearest inspection cover and see whether that restores normal flushing and also that the flushed water comes past nice and briskly rather than as a trickle. If so, your problem probably lies downstream. If not, it's between the loo and the inspection cover. Divide and conquer.

[BTW, I don't like internal AAVs much. I don't really do drains but yours looks a bit low to me, have you checked the manufacturer's installation instructions?]

Hope so, they look like they are in the floor.

 

[Chuck]

Hope so, they look like they are in the floor.

Good catch! FIxed. Thanks.

 

[Paul Cockhill]

Air admittance valves only fix issues arising from negative pressure in the drain. If you have a downstream blockage you'll get positive pressure and the symptoms you describe.

Lift the nearest inspection cover and see whether that restores normal flushing and also that the flushed water comes past nice and briskly rather than as a trickle. If so, your problem probably lies downstream. If not, it's between the loo and the inspection cover. Divide and conquer.

[BTW, I don't really do drains but I don't like internal AAVs much and yours looks a bit low to me. Have you checked the manufacturer's installation instructions?]

HI Chuck

Thanks for the reply. Yes I think I might have to raise the level of the AAV and see if that makes any difference. I will also look further downstream to see if there is any other blockage. I dont think that is the problem because the bath and washbasin are emptying no problem.

when I take the AAV off and flush the WC the water flows quickly and with no problem

Thanks

Paul

 

[snowhead]

You've definitely got a partial blockage downstream.
The flow from either the bath or sink is less, so the issue doesn't show.
All that lifting the AAV does is to allow more space in the pipe for the water to occupy, by allowing trapped air out.

As you lift the AAV you will either feel a draft or smell the air coming out .