An air admittance valve (AAV) is a one-way valve that allows air to enter the drainage system without allowing sewage gases to escape. AAVs are commonly used in situations where it is not possible or practical to install a conventional soil and vent pipe (SVP).
While AAVs are a reliable and effective way of dealing with ventilation, they can sometimes fail. The most common reason for failure is blockage. This can be caused by debris, such as leaves or toilet paper, getting into the valve and blocking the airflow. If an AAV becomes blocked, it will no longer be able to ventilate the system properly and sewage gases may start to escape.
Another reason why an AAV may fail is due to corrosion. Over time, the metal components of an AAV can become corroded and weakened. This can cause the valve to leak or even break completely.
If you think your AAV might be failing, it's important to get it checked out by a qualified plumber as soon as possible. They will be able to diagnose the problem and find the best solution for your situation.