pressure overflow problems on Thermaclassic combi boiler,?

Hi, I have had the prv on my boiler replaced as the overflow pipe was dripping and the pressure dropped to 0.0 when the heating switched off. This hasn't solved the problem

I have noticed recently that the overflow is still dripping (at quite a rate sometimes) but when the heating swtiched off and the pressure dropped to 0.0, I topped up the pressure to 1.0 and left everything but when I returned 2 hours later the pressure was up to 2.6.