radiators?

All the radiators are bottom fed so why do 6 of 14 get hot first at the top progressively getting hot downward. Where as others heat from bottom up, all I get on opening the rad air bleed point is WATER no air. On an exention pipe in the pump piping is what I've been told an auto air valve, which I assume where the air is dispersed hence none in rads. Could this heating of radiators top first be the system hasn't been cleaned properly last year when we had our boiler replaced. We were charged for power clean.