how can i fix my glowworm swiftfow 80?

every time i turn the heating on, it starts up fine but only runs for about 10 min`s then goes out but the pilot goes out too? i spent the other night re-lighting the boiler every 15 min`s because of this (and it was too cold not to!). the hot water works fine, it`s just the central heating. the fan was recently replaced and all worked well up till this week ??