Caffeo Solo - water quantity regulator without function

Hello all,

Have a Caffeo Solo which hardly makes coffee. It always comes out about 20ml of coffee.
No matter how I turn the water volume control, it remains at about 20 ml.
It is also irrelevant whether I press on 1 or 2 cups, the amount that comes out in front is always about 20ml. I am somewhat at my wit's end.
Machine is decalcified, clean and otherwise runs smoothly. When rinsing, the amount of water has actually not changed much, only when drawing coffee.

Drainage valve is new and nothing runs into the bowl anymore. I can rule out the problem.

The only remaining cause of error is the controller itself or the flowmeter.

But before I replace one part after the other, here's the question in the round, whether someone had this before.

Greetings and thanks for the help