How can I fix my vaillant combi boiler?

http://www.youtube.com/watch?v=_Pf4qF6w68M

Q
December 2013

It's running dry fill waterto 1.2bar from filling loop right under boiler with radiator key it echo tec two white nob open and close if you are not sure refer to boiler manual,vent all radiators ,open big silver nut on pump let water out ,it may take 20 mits to clear air ,why water lost to be investigate it from pressure relief valve need new one

ltd
November 2013