Boiler kettling – It seemed that F1 protector it supposed to help with this, but it seemed putting that in caused trapped air and other nasty reactions.
Expanding / shrinking pipes – This sounds like it could indeed be the case. As I can lift and move my radiator slightly and feel it rubbing in the hole in the floorboards, and I can almost create the identical sounds myself by doing this. However, the radiators and pipes have not changed since our boiler got replaced, so as that is the case, I can’t understand why this should be related. Our heating with our old boiler just bade a very quiet and consistent tinkling while on, and no noise when off.
Dirty pipes – While we had the F1 protector put in supposedly to clean the system, given the reaction it caused, it probably has made it worse. We don’t have air / gas in the system now and the water seems clean, but I obviously can’t tell what the pipes are like. I don’t believe it is related to the radiators now, as I can turn them off at both the TRV and other valve and the noise still occurs from the pipes.
I had said in my original post (sorry for the length of if) about me thinking it could be expanding pipes, although I thought several things me and others had discussed since sort of made this unlikely. As the pipes and radiators haven't changed since the new boiler got put in place. And this clicking and banging only got introduced when the radiators got refilled with F1 protector a year ago. Almost all the pipes seem to do this now (but vary in volume), when they didn't before the system got bled out.It could be something as simple as heat expansion due to the little plastic radiator clips breaking at the back where it goes onto the metal bracket