Pressure gauge at 6 bar! What is wrong with system?

I have an Ideal Classic boiler with a sealed system which was installed 14 years ago. In the last 3 years I have replaced all 6 radiators at least once due to leaking. I have also replaced the pressure gauge, the actuator, the pump etc etc in the same time period. I have just had the boiler serviced and yet I have a major problem in that the pressure gauge is hitting 6 bar and the radiators are over heating. Can anyone tell me what the problem is please?