I have a Vokera combi that keeps lossing presure only when I use the centeral heating. I have changed the PRV. I can take the pressure up to 3 bar when the system is off and will not lose any presure. But the presure will go from 1.5 to 0 after the ceteral heating has been running for 3 hours then once the water has cooled.

Ian G., March 2009