The central spout dispensing unit is not correctly installed or is wrongly assembled.
Remove and dismantle the parts of the central spout.
Clean all parts of the central spout if necessary.
Reassemble the central spout parts in the right order and reinsert them into the coffee machine.
Removing, dismantling, reassembling, and inserting the central spout:
Carefully pull the stainless steel cover forward and off.
Remove the dispensing unit by pulling it forward.
Twist off the upper section with the holder for the milk pipework. Pull the component off.
Then pull the Y-shaped piece off.
Remove the dispensing spouts .
Reassemble the dispensing unit as follows:
Push the dispensing spouts firmly back onto the dispensing unit.
Reinstall the Y-shaped piece .
Reinstall the upper section with the holder for the milk pipework. Turn the component.
Reinstall the dispensing unit onto the central spout.
Reinstall the stainless steel cover.