How can I fix Ariston micro GENUS HE type C 28kw boiler?

How to correct the following condition.
Boiler as specified. Commissioned March 07. Therefore just out of warranty.
Boiler has shut down displaying A 01.
Basic fault finding followed i.e.
Check flame failure works - checked ok
Check pressure switch closing - checked ok
Check gas pressure - checked ok
Check good earth contact - checked ok
Other info = press reset button and boiler fires up for 7 secs then shuts down displaying A 01.
The ignition electrodes are sparking for the whole of this duration.
On supplying power to the boiler 6 HE is displayed.
Any ideas ?