Possible causes	Recommended action
Unbalanced power supply voltage.	Contact the electric power company and take measures.
Large voltage drop	Contact the electric power company and take measures.
Open phase	Inspection of wiring connections and magnet switches
Pump for 50Hz is operated in the 60Hz zone.	Check nameplate and replace the motor.
Pump operating in reverse rotation.	Change the rotating direction to the appropriate way.
Pump head is low. Excessive discharge quantity.	Close discharge valve to the specified water level.
Pump is clogged.	Disassemble and remove foreign objects.
Damaged electric motor bearing	Repair or replace