Frequent starting leads to excessively high temperature, overheating protection of the soft starter thereof operates (starting frequency of the soft starter shall be controlled within 6 times per hour, particularly in heavy load). Protective elements act at starting, which makes the contactor unable to by pass, the soft starter works for long time and thus causing the protection to act (check peripheral circuit). Heavy load and long starting time lead to overheating protection (reduce load as far as possible when starting). Parameters of soft starter are improperly set. Long starting time and low starting voltage (increase the starting voltage). Radiator fan of the soft starter can't work normally (replace a fan).