Siemens EQ.9 700s extraKLASSE runs out "directly" !

Hello,
In our MWF, the water runs directly into the collection tray after the water tank is inserted. No matter whether it is switched on or not. That is, it drips every second from the opening expansion chamber, until the collection tray overflows
Does anyone have an idea what is wrong here ?

I have tried the following:
Since the pump sounds completely normal, and it also otherwise does what it should,
I have tested where the water comes from. The source is the hose ceramic valve ---> expansion chamber. So quickly dismantled the ceramic valve, disassembled and reassembled, but it looks inside and outside completely inconspicuous, no "dirt, no calcification. The pummpe was therefore inevitably out. Everything zsammengebaut again and tested. It drips in the switched on as well as switched off condition in the second cycle into the collecting tray.

Thanks and greetings
Tom

Ok, doesn't seem to be of interest here.