How do I mend my Vaillant Combi Boiler?

It has stopped from heating water both for the taps and the radiators.
Pilot lights are still on, and flame in viewing window can be seen but does not "burn" as it normally does during previous use.
I don't know if it is related, but a couple of days ago I openned the valve to restore the pressure back to 1bar since it was below it. On the succeeding days, pressure went above the redline (2.5 bar) almost reaching 3bar when heating was being used.