HOW DO I FIX MY BAXI SOLO 2 40PF BOILER?

I HAVE AN ISSUE WITH MY BOILER AS FOLLOWS. IT POWERS UP, SWITCHES ON THE FAN, LIGHTS THE PILOT AND THEN THATS IT. THE BURNER DOES NOT FULLY IGNITE AND SO NO HOT WATER OR HEATING. DOES ANYONE KNOW WHAT THE PROBLEM IS AND HOW I CAN CORRECT IT PLEASE? WHEN THE PILOT IS LIT IT KEEPS CLICKING AND SPARKING AND THE PILOT IS LIT, GOES OUT AND IS RE LIT AGAIN. COULD IT BE A TEMP SENSOR FAULT OR MAYBE THE GAS VALVE? PLEASE HELP ASAP IF YOU CAN.
THANK YOU