sime 80e friendly format ,start,stop,start,stop etc?

Hi my boiler has just started playing up ,put heating on ,fan runs ,ignitor fires up gas for about 5 seconds then flame goes out ,fan stays running ,igitor fires boiler up again for 5 secs and goes out ,keeps repeating this cycle .same with hot water .has anybody got any idea what it could be ??? i replaced control unit 2 years ago