Air Admittance Valve

[Driver]

We have an air admittance valve on the top of a waste stack outside a first floor a bathroom. The valve is about 50cms above the waste inlet from the toilet. This has been there for 20 years plus and has never been a problem. About a week ago when the toilet was flushed the water rose up the bowl but did drain out quickly. I thought we had a blockage and used a plunger to no avail. Since then I've had 2 plumbers look at it who both used a plunger again to no avail. However the second one took the air admittance valve off the stack and then when the toilet was flushed it emptied as normal.

I have now bought a new valve but the problem remains the same. With the valve off the toilet empties normally, with it on the water rises up the bowl.

Any suggestions anyone.

 

[lambchop]

Nice one chris, quite right. I was wrongly under the impression that an AAV has the ability to vent if experiences a high level of positive pressure (I must have stuck my pinky in the wrong way when I defiled my last aav). I do understand as stated in my op that there primarily for letting in air. There are PAPA Positive Air Pressure Attenuators for dealing with these situations

 

[lambchop]

forgot to 'like' your last comment! got to take my medicine lol