Issues with Air Admittance Valve – Plumbing Q & A ©Depositphotos.com/Goodluz Question– “Why would an air admittance valve discharge a sewer odor that is only two years old?” Answer – It’s mechanical and it appears that it is failing. In our opinion, you should have the air admittance valve replaced. Ask the Plumber2018-03-05T18:10:42+00:00