I have a Glow worm compact electronic boiler, ?

What does it mean when the only way i can get my boiler to work is by tapping the bottom right hand side panel in the corner next to the on/off switch. The two green lights for heating and ignition are lit, then once the unit has been tapped the 'flame' light comes on and the unit starts to work providing both hot water and/or heating. This will happen every time i need to use it. It has been regularly serviced.