how to ignite pilot light on worcester 240?

I have viewed the answers to this problem on your site that identifies a grey knob and red button but there is no grey knob or red button. I have tried the grey button labelled 'heating advance' to no avail. I looked at the worcester site and the advice was that a professional should do it for me. Also the pressure is slowly increasing (now at 2.5) I've bled the downstairs radiators but not emptied them as I don't know how to re-fill. Unfortunately I can't afford a plumber - can you help? Thanks in advance