My husband and i have exactly the same problem today and looking on a post on here managed to get it working. All be it that we were petrified of blowing ourselves up!!!
Turn your boiler off at the mains (electric switch), but leave the pilot light on as well as the central heating switched to on.
You need to remove the front casing from the boiler. then locate the 2 yellow wires that go into the same white clip. Remove this clip.
Turn the mains back on. Your boiler should fire up immediately.
Leave for 1 - 2 mins. Then switch back off at the mains. Once this has been done. put the yellow wires clip back into the relevant place. We blew on our plug first incase of any dirt. Then turn mains back on. Voila should be back and running OUrs was. The replace all the coverings.
Hope this helps you
KFITZ090509, November 2009