The central spout dispensing unit is not correctly installed or is wrongly assembled.
Remove and dismantle the parts of the central spout. Assemble the parts again in the correct order.
Proceed as follows:
Remove the stainless steel cover to the front; see Fig. 1.
Pull the dispensing unit forward to remove; see Fig. 2.
Twist the top part with the holder for the milk pipework. Pull off the top part; see (1) in Fig. 3.
Pull off the Y-piece as well; see (2) in Fig. 3.
Loosen the dispensing spouts; see (3) in Fig. 3.
Reassemble the dispensing unit; see (4), (5), and (6) in Fig. 3.
Push the dispensing spouts firmly back onto the dispensing unit.
Reinstall the dispensing unit onto the central spout.
Put the stainless steel cover back into place.