Glow Worm Micron 50FF - boiler fires from 'cold' and stops after 90 secs?

This morning, my boiler showed no fault lights but appeared to have fired up but then stopped running.

After a few tests to try to identify where the fault lay, I deduced that it simply fires up from 'cold', but stops running after approx 90 secs.

It then refused to fire up again until it had 'rested' for about 20 mins.

After 4 hours of fiddling and trial and error, I've managed to get it running again and holding this time.

Do you know what may have caused this issue, so I can be more prepared to handle the issue if it reoccurs in this Arctic spell!

Thanks