Ferroli Optima 901 Problem

Hi

Any help with this problem would be greatly appreciated.
Got a Ferroli Optima 901 combi boiler. Drained system to install a few new radiators. Refilled system. No air in system as far as I can see and its pressurised to 1 bar.
Ive relit the pilot light loads of times previously so I know how its done. But now it just wont relight. On turning knob to heating continuous/hot water you hear pump/fan start up as it should but then after waiting the 20seconds pressing the gas ignite button causes the whole thing to shut down. You may hear one or two clicks of the igniter then nothing. Also most of the time when I turn knob to continuous/hot water nothing at all happens not even a click of the igniter.
So have I not done something which I should have when refilling system? I actually did nothing to the boiler when refilling system. Just got air out of radiators and pressurised system to 1 bar.

Thanks
Chris