Random F1 error on Glow Worm 30ci?

Our boiler is a Glow Worm 30ci model, and it has been random F1 errors from new. After several repair men said they had no idea what was wrong, all we can do is guess at causes, such as there seems to be a breeze coming through the unit - could this cause it? Also it seems to only happen on particularly cold days. Any ideas folks - I hate to leave the cats in the house for a few days (with a cat sitter) with a heating system that is playing up! This is the worst it's been - it's been going on for days. Thanks a ton for your help!

Rachel
November 2008