had a few problems with gas boilers before, can you tell me if there is a clear inspection panell on boiler, you should be able to see gas flame when boiler works correctly ?
if so, can you see the pilot light working ?
if you can issue could just be an air lock in a gas supply tube, either that or pump for gas.
if you can hear a clicking sound, but cant see a spark then the spark generator (not the correct term) if failing to spark...
there is a reset button, normally on underneath of boiler, could look like a small plastic rod, this may work, and it is probably the only thing you can try without calling someone out...