A method for starting a motor (14) with a bidirectional rotation direction, to rotate a fluid circulation centrifugal pump (10) having a predetermined optimum hydraulic efficiency depending on the starting rotation direction thereof. The method provides an initial motor (14) starting in either rotation direction, with subsequent pump (10) rotation in the same direction and, subsequently, a periodical interruption and restoration of the motor (14) power feeding as many times (N, N') as to ensure the motor (14) starting, at least one or more times within a predetermined time interval (T.sub.tot, T.sub.s), in the rotation direction which corresponds to the predetermined pump (10) optimum hydraulic speed.