Do it again with the pump off. Make sure the valves are open at both ends. Make sure the supply to the CH circuit is active – either the small tank in the attic or the pressurising loop below your boiler.
If a rad still doesn’t work, turn off the valves, loosen the valve to rad connectors, lift the rads (they are heavy) off the brackets and swivel them down to the floor. Undo the connectors fully and turn the rads upside down then take them out to the garden and allow all the filthy black sludge to drain out, then hose it out. Keep those rads upside down indoors though, unless you want black splodges all over the floor.