Aeg Favorit 50730 Anti Flood Device

This machine works well but has recently developed a recurring problem of triggering the anti flood device and becomes inoperative.

As I was unable to actually do anything to reset and stop the two flashing lights I called a service engineer. He explained that it is not usually the valve on the inlet pipe that fails but generally a blockage in one of the pipes.
He apparently disconnected some hoses, did something and put it all back together and it worked fine — for a week.

Naturally I found it difficult to understand how this could happen again especially after I had run a washcycle using one of those “clean the dishwasher fluids” after hisvisit.

Anyway I examined the pipes couldn’t find a blockage. However on the
right hand side of the machine is a brown circular device with a vacuum
hose. If that hose is disconnected and then reconnected a vacuum is released and the anti flood device is reset. Fine. but now the machine will run 2 or 3 times and then the anti flood will be triggered again and I have to take the side off and reset the vacuum, which is a real pain.

There is no debris at all in the sump below the filter, the filters are clean.

On watching the machine working, the anti flood device gets triggered at the end of the drying cycle, not at all when water is entering or leaving the machine.

Please does anyone have some advice on how to search for whatever the problem is or how to disconnect/bypass the antiflood device.