We've got one of these and it's been a nightmare. General fault description would be pump running, 'boiler on' light on, but no burner.
Air pressure switch, thermistor, fan and PCB all changed which fixed it for a while then back to the same old symptoms and no heat. Mate who is CORGi gave up replacing parts only to see the problem come back a month or so later, and he told us to get British Gas in on their fixed price deal. Apparently he makes enough cash just installing new boilers that he doesn't want to spend unpaid weeks going on training courses on how to diagnose and fix them. Whereas BG send their guys on training courses all the time and so know all the boilers and their problems.
So BG man comes in, spends 2.5 hours replacing fan, thermistor, air pressure switch and PCB. Says it's fixed and fires it up, and the thing almost burns his hair off. Says this wasn't right, and looks some more, and finds the flue had missing parts. According to him the airflow coming into the boiler was all wrong, combustion was all wrong, and the boiler was overheating and frying the parts we had replaced within months.
So he disconnects it and heads off to get the part.
Came back few days later, 1.5 hours working on it, most of it cussing and swearing because he was trying to get the flue gas mixture safe.
Signs it off as safe, tells us the wiring is all wrong but cannot put finger on why, and best thing to do is change it.
So, it wasn't put in properly in first place, and the same heating engineer had serviced it and just got it all wrong. We bought the house 12 months ago and saw a receipt for boiler which says it installed new three years old. BG man says it's more like eight years old.
Seems to be working fine for now.
Apparently the usual cause for the original symptoms is faulty air pressure switch/connectors, or bad fan, in that order.
Great value from British Gas. Only time I can think of that I can say that.