Problem with Glow Worm 30 Ci boiler?

I have posted a similar question but still with no answers. Anyone out there with any ideas? My Glow worm 30ci is playing up. The water temperature fluctuates from cold to warm to cold to hot to warm to cold etc. The burners operate and seem to ignite and light fully, but then they extinguish after a few seconds before igniting again , and going through the whole process again. Thus i can hear the flame igniting many times in a few minutes which i have not heard before. Any ideas?? Thanks, Will