hi
best to repressurise when system cold
slide white plastic cover plate off (underneath bottom of boiler)
there should be a plastic T key clipped to it
take key off, look under the boiler and to the right side theres a black plastic assembley with a white square screw, a hole ( where you put the barrel of the T key) and a black cap.
look carefully at the key there should be an arrow head marked on the handle look at the hole where the key fits there are two symbols of pad locks on it, one is unlocked the other locked. line the arrow on the key up with the unlock symbol push the key in as far as possible and turn so the arrow head lines up with the locked symbol turn WHITE screw anti clockwise to fill boiler to 1.5 bar close white screw fully, take key out replace key and cover. simples
ps page 33 of installation and service booklet (should have been left with boiler)