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When flushing the toilet it is slow to drain and air bubbles up through the shower drain. If I remove the air admittance valve all works correctly.
The current aav seems to be opening and closing but does not operate when fitted. I have tried a replacement aav and the fault remains, however the valve was bought online and the box was damaged. Is it likely that both aav’s are faulty?
Thanks in advance.

Hi bill50,
Presumably you do not plug the hole where the AAV is fitted for the second of your tests. I also assume you have an open stench pipe at the highest point of your soil system. Most likely that there is a defect in the falls on the main soil pipe or you have a partial blockage. The problem will be finding it.
Regards S

Thanks very much for your response. I was thinking the same thing as the fault is intermittent and also Southern Water are regularly “fixing” drainage problems in the area.

Hi bill50,
Unfortunately water boards generally seem to have a sticky plaster approach to problems, hope you get your sorted.
Regards S