The milk valve is clogged.
Clean the milk valve as follows:
Open the appliance door.
Remove the bean container and maintenance container on the left-hand side.
Remove the central spout’s stainless steel cover.
Remove the milk valve cover as follows: On the top right-hand side of the cover, you will find a pin for swiveling the cover out.
The milk valve cover should only be cleaned by hand.
Detach the milk pipework from the dispensing unit on the central spout (1) and from the milk valve holder (2) and (3).
Remove the milk pipework (1) connecting the milk valve to the central spout.
Disconnect the angular molded hose from the round hose.
Rinse the hoses thoroughly under running water.
Do NOT remove the connecting pieces from the hoses.
Press the latches on the left and right-hand sides of the milk valve holder. Pull the holder forward to remove it.
Take the holder and silicone seal apart.
Pull the stainless steel bolt upward and out.
Clean the individual components of the milk valve in the dishwasher.