Why does my Baxi Bahama flame out ?

I have a Baxi Bahama wall mounted boiler which flames out four or five times a night when the CH is on. It does not do it during a burn, only when it tries to start. I have had two repair companies look at it and both have gone away with no answer. I think that his because they are only familiar with mechanical problems. Anyone had similar problems or have any ideas?

Fed-up
November 2010