I know nothing of boilers - I am an unqualified muppet - my advice is potentially dangerous.
When the bolier gets a call for heat the control board supplies power to the fan on two red wires terminals 7 & 8 on the control board. There should be 230V betwen them at this tme.
The fan is monitored by an air pressure switch - the switch must be made for the boiler to light up and remain running. If the fan fails or begins to fail the air pressure switch will signal the control board to shut down.
Your boiler shut down spontaneously. On restart the fan ran but the boiler soon shut down again. Now the fan no longer runs.
Most of the symptoms you report point towards the fan. My simple uneducated analysis is that the fan's bearings are (have) siezed up. Your earlier intermittent running was happening just before they finally gave up.
No warranty expressed or implied in this answer.
Good luck...
Peccavi
March 2010