worcester 24i junior?

you may need a key to insert between the two plastic knobs under the boiler into the black filling link. (black/white knobs or grey.)open the white one very slowly and pressurise to 1.25 bar WHEN COLD.Close and remove the key.do not over tighten the plastic screw nut when closing off inlet (they can break).A drop of water may come out when removing the key. Should show you in the customer use manual.Any doubt always get a plumber.

kev
May 2013