Potterton Suprima 70....lound banging and frequent lockouts?

I have a Potterton Suprima 70 Boiler.
Frequently get loud banging noises.....almost seems as if the boiler is about to jump off the wall. Pretty scarey noise. Also frequently locks out.
Had engineer in this week He changed the PCB. Needless to say the noise didn't occur again until after he had left......and the boiler is locking out more frequently than before. Five / Six times a day. I seems to be looking at the control; panel more than my TV. Two thermostats were changed in the boiler about six months ago. Any ideas what the problem could be?