DIAGNOSIS The opener is detecting an obstruction during its closing cycle. The most likely cause is misaligned safety reversing sensors.
FIX First, verify the sensor alignment. The indicator lights on both sending (yellow lens) and receiving (green lens) sensors must be solid, not blinking. Use a level to ensure both sensor brackets are aligned horizontally. Adjust the bracket if the light is blinking. Clean the sensor lenses with a dry cloth. Test the door operation.
IF THAT DIDN'T WORK The force setting may be set too low. Check the force adjustment dials on the side of the motor unit. The down force dial should be turned clockwise slightly to increase the closing force, but no more than a quarter turn at a time.
HEADS UP After adjusting force, perform the safety reversal test. Place a 1.5-inch block of wood on the floor under the door's path. The door must reverse upon contact. If it doesn't, the force is too high and must be reduced.