Worcester Bosch 350 combi boiler loosing pressure?

We have a combi boiler that is about 12 years old. Every morning the low pressure light is displayed and we have to top up the system by turning the key to 1.5 to 2 bar pressure to enable the system to become active.

When the heating is on, water is discharged through the overflow pipe outside.

We have add the safety valve replaced, but this has not fixed the problem.