The central spout dispensing unit is not correctly fitted 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 forwards.
Twist off the upper section with the holder for the milk pipework. Pull the component off.
Then pull the Y-piece off.
Remove the spouts .
Fit the dispensing unit back together as follows:
Push the spouts firmly back onto the dispensing unit.
Refit the Y-piece .
Refit the upper section with the holder for the milk pipework. Turn the component.
Refit the dispensing unit in the central spout.
Refit the stainless steel cover.