we have an F9 fault showing ?

when we go into the boiler and on advice try to up the water pressure, it just gushes out and will not go over 0.9 bar, an engineer has been out and said this boiler is prone to leaks that this happens all the time and that really its the circuit board that is the problem, as this is not my normal engineer I am a little worried, could this circuit cause an F9 fault?????