Basins with push button wastes not emptying

[Tomfromsurrey]

Hi, I have purchased a new build property, which has a family bathroom, cloakroom and 2 en-suite shower rooms. All 4 basins have push button wastes in the basins. The 2 en-suite basins have a problem…. Waste push button is up, so open. Run the tap and the basin starts to fill even though the push button is up (open). Push the push button down to close the waste and then again to open the waste and the water drains away. This happens in both en-suite basins but not the family bathroom or the cloakroom basin. All are the same push button wastes. All traps are clear. Swap the push button waste from the family bathroom to the en-suite and it fails in the same way in the en-suite but the waste that failed in the en-suite works fine in the family bathroom.
The 2 en-suites are on a different soil stack to the family bathroom and cloakroom. Both soil stacks have AAVs on them. The AAV on the en-suite stack was removed as a test but the basin drains still fail. All the basin pipework is under the floor an inaccessible. The pipes and the basin waste units are very clean. The rodding point outside has been uncovered but the problem persists.

The plumbers don’t know how to fix the problem. Has anyone seen this problem and have a resolution?
It appears to me that there is pressure in the drain pipe holding the water in the basin?

Thanks for any help

 

[Deleted member 120897]

Could be a backfall an pipe under the floor, partial blockage or the slotted waste holes that connect to the overflow not lined up.

 

[Tomfromsurrey]

Also see my other topic Gurgling shower drain - https://www.plumbersforums.net/threads/gurgling-shower-drain.122894/

Problem in same en-suites