Had a similiar problem, my boilers in the garage and gets a bit damp too. I gave it a good clean up inside and checked the flame failure probe which appeared ok, but it did have a lot of residue & dust inside. I checked all the connections and after a few attempts it started working again. I think boilers need a service once a year by a professional, its worth the cost, find someone who is recommended.
G Pilbeam, October 2008
