Ravenheat CSI 85 or 85 T broken?

Hi ive been trying to sort my boiler out i think its out of my league but i want to know if its fixable so the flame failure light keeps flicking into gear i can hear it rumbling but never actually fires this is after the point of it going through constantly trying to fire then eventually doing it say a 1 in 20 oddly enough hitting brought few results boiler wise at least and if it is fixable what do you think the problem is would love to hear your ideas