How can I fix my ACO boiler?

My ACO 32 MFFI 47 also keeps banging like a car exhaust going off. I've just had it serviced, and it was OK for a couple of weeks but now its started again. Its very loud, wakes me up, sounds like the ruddy boiler is going to jump off the wall, and the warning signal is, yes you've guessed, AO7
Please can anyone advise with this as I don't know what to do.