How can i fix my Glow worm KFB 60 open vent boiler. ?

When the remote controls are calling for heat, neon 1,2,3 & 4 light up indicating that system is functioning correctly, however in a very short time neon 4 goes out, only to reignite itself again almost immediately, this can happen maybe eight to ten times It may run OK for it's duration, only to do the same process again. I have gone through all the fault findings in the manaul including a replacement board . Any advice.