pressure problems with worcester 24cdi?

The pressure relief valve keeps dripping, as a result the pressure drops. Also the pressure goes from 1.5bar to 2.5bar when the heating is on, which then makes the valve drip more. cant get the valve out due to the side of the boiler in the way. the only way i can see to get it out is to disconnect half of the boiler to remove the whole plastic fitting that it is all connected to.
Can anyone give me an answer.