You need the key, which should be attached to the bottom cover (slides out) - The key then goes into the valve on the underside of the boiler (get your head down and look up!). Note it needs a right good push to engage the key into the slot properly!
Turn the key to the 'unlocked' position then turn the knob beside it to allow water in to re-pressure the system. Fill to 1.5 bar then turn off, turn key back to 'lock' position, and withdraw. Good luck.
CMac, December 2010