When a system is fully primed, the system components, pipes, pump, filter etc., are filled with water and the pool pump is able to suck water from the pool and push it back into the pool through pool returns. Priming a pool pump involves purging air from the pumping system and filling the water lines and pump with water. The number of steps required to prime your pool pump depends on the amount on water in the suction side of the lines - water coming from the pool to the pump. If you are installing a new pool system, there is no water in the lines, and you may have to repeat these steps several times. If you are adding or replacing components into the pumping system (like a heater), there will still be some water in the lines and priming will be simpler. The following procedure assumes that you have no or little water in the system. Visible indications of low water are no or little water in the pump strainer box, and a low pressure reading on the pool filter pressure gage.