does the system need bleeding ? if when the heating is on the radiators are hot at the bottom, but stay cold nearer the top, you have air in the system. if the radiator is turned on, but stays cold. again probably caused by air, in the pipes. any banging noice can normally be traced back to air. it sounds worse a problem than it is, it is the echo which makes it so loud.
it's easy to bleed the system, at the top of each radiator is a valve, older ones you will need a special key, new ones a small screwdriver, hold a towel over while you undo it, you will hear the air come out, when water starts coming out , tighten the valve. go around all the radiators in turn, starting with the one furthest from the boiler, and finishing with that nearest the boiler.
you may need to do the whole system a couple of times, but bit by bit the air should all come out.