The blue light flashes differently depending on the fault. However, when I had this fault recently it was a blocked condensate syphon. Not a big problem to sort out but a bit fiddly to get to the screws that hold the plastic syphon assembly in place, The pipe coming out of the bottom centre and going into some local waste system is the condensate drain pipe.
Unfortunately my wife has just phoned to say now a different fault. Blue light was flashing but remained steady on reset. However, greeen light ('burner on') will not stay on. Anyone haver any ideas?
Ian
January 2010