How can I fix my Vaillant Turbomax Plus combi boiler?

Have recently drained and refilled system. Turned boiler on and after an hour or so pressure was around 2 bar, and remained there. Then I turned the central heating off for a few days.Then turned it back on again and pressure was well past 3 bar on the pressure gauge. Is this normal or is there a problem. I have heard that system pressure should be no more than 2.5 bar when system is running normaly. Is this correct? Would be very grateful for any views on this.