Ideal sealed boiler?

sound silly but
Sealed boiler with loop topup does this loop also serve to fill the system when drained I can't see any other way to fill it? do I have to vent each rad as a friend said in the airing cupboard upstairs is an air bleed valve on a tee off one of the 22mm the pipes. Will this vent all the air out of the system without having to go around each rad?