the best way is to turn the boiler thermostat off then turn the c/h and h/w (do c/h first as it's the easiest one, then add h/w in, then h/w alone, if still loads of air put c/h on at same time) on and off when ever you hear air going through the system, this will take a up to about 30 mins. this stops the boiler firing and helps shift any air in the system, it's the best way to clear air. then bleed the system it runs nice and quiet. turn the boiler thermostat back on and away you go.
i know some people do it but i've never had to resort to turning a pump around before, it's just creating more work for yourself especially if you've got ball type pump valves that are rubbish and will leak or the valves won't properly shut off.
if the boiler fires it's harder to clear the air unless it's a gravity system, in which case remove the boiler thermostat phial from the boiler and let it overheat on h/w as this is the best way to clear the air lock