MUNCHKIN MC99 BOILER

[MER57]

HAVE A MUNCHKIN MC99 BOILER KEEPS SHOWING A F10 CODE THE BOILER HAS HAD COILES CLEANED YEARLY. I HAVE CLEANED FLAME SENSOR & IGNITER NO LUCK EVEN REPLACED SENSOR SAME THING. RUNS GOOD THEN ANOTHER F10 CODE. FINALY TODAY I RESET IT WHEN THE BOILER CAME BACK ON THE GAS FLAME WASN'T STEADY IT WWAS PULSATING UP AND DOWN THEN ANOTHER F10. RESET IT RUNNING FINE NOW. IT LOOKS LIKE THE FLAME IS BEING BLOWN OUT. ANY IDEAS HOW THIS IS HAPPENING?