A centrifugal pump assembly has an electric drive motor (2) and at least one impeller (10; 10′), which is movable in an axial direction (X) between at least two functional positions. In one functional position a flow path through the impeller (10; 10′) is essentially closed and in another functional position the flow path through the impeller (10; 10′) is opened. The impeller (10; 10′) in a first functional position is held by a magnetic force (FM) or a spring force and in a second functional position is held by a hydraulic force (FH) produced by a delivered fluid. An impeller is provided for the centrifugal pump assembly.