-
Something ain’t working. Got enough water in the u bend? Sure the pipe work is good? Is the one way valve on the valve stuck open?
Are you sure yours is done right?.
Air admittance valves, when installed, must finish above the highest flood level of the space the valve is in. E.g. If the valve is in the same room as a wash hand basin, it must be higher than the overflow of that basin. This is so the pressure equalisation can occur without breaking the water in the traps
(It might be sucking the water in your basin trap away allowing foul air up through the sink)
It looks like a durgo value, you use it to ventilate the soil pipes and stops smells coming into the room. Hence why you get a smell when its off.