The brew unit filter is slightly blocked.
Clean the brew unit of the coffee machine once a week by hand.
Proceed as follows:
Disconnect the coffee machine from the power supply.
Open the appliance door on the right-hand side of the coffee machine.
Press the button on the bottom of the handle of the brew unit; see (1) in Fig. 1.
Whilst doing so, turn the handle to the left; see (2) in Fig. 1.
Carefully pull the brew unit out of the coffee machine.
Clean the brew unit by hand under warm running water without using any cleaning agent.
Wipe any coffee grounds off the filters; see Fig. 2, Fig. 3, and Fig. 4.
Clean the brew unit with a cleaning tablet for degreasing using the Degrease brew unit or Clean brew unit maintenance program.