potterton suprima 40?

i h ave a potterton suprima 40 which has working fine, but the other night whilst the heating was on, there was a quite loud humming/buzzing sound from the boiler, the boiler had gone out, on trying to relight the boiler the fan cut in as normal, but then there was this noise seeminly coming from the right hand side of the boiler, and no gas lit up, the then went to lock out, this procedure can be repeated, any ideas??