I asume you have solved this problem by now, but have just had a similar problem myself, now solved with the help of another website, complete with diagram!
1 - switch heating control to 'O'
2 - switch main heating control / timer switch to 'on'.
3 - on top of the grey bots, which has a load of pipes / wires coming out of it (above the pilot light hole) there is a grey knob - on the top of this is a symbol which looks like a flame, and a clockwise arrow - yes we missed it too yesterday! Turn this to the right and release it immediatly.
4 - put your light / gas lighter etc into the hole and click it to ignite whilst holding down the grey button you just turned. Keep the button pressed in even if it doesn't light first time.
5 - Once lit, hold bouuon in for another 20 seconds then let go and check pilot light is still on.
6 - now stitch the control you put on '0' at the start back to where it was before (mine was set at just under 3). You should hear the main boiler / heating cut in now.
If it doesn't work you have to turn the knob and release it again, then wait 3 minutes before repeating the procedure. Mine worked the second time around, but that may have been me!
Heating now on and I'm finally warming up .
Good luck and thank God for the Internet and websites like these
Val, September 2010