A motor with associated load sensor is connected to a circulation pump of a swimming pool circulation system. The load sensor performs the function of a safety vacuum release system by detecting underload of the motor. Underload is now discovered to be reliably indicative of blockage on the intake side of a circulation pump. A switch controlled by the load sensor shuts off the motor in response to a suitable underload. Vacuum on the intake side of the circulation pump neutralizes, thereby freeing a person or object blocking the suction line.