The garage door opener has two mechanisms that control the opening and closing of the garage door. One is the safety reverse mechanism that will stop the door operation in the event something obstructs the door. The opener also uses limit switches to determine how far to open and close the garage door. When the garage door does not open all the way or does not seal to the floor when closed, you can reset the limit switches. Resetting the limit switches is not difficult and require only one tool.
Place a step ladder under the garage door opener motor. Locate the limit switch screws on your unit. Most switches are on the back of the motor head, while others may be behind the light bulb lens cover. The switches are two white knobs with a slot for a flathead screwdriver.
Ask a friend to operate the opener push button on the wall to open the garage door. The bottom of the garage door should be just below the door opening header.
Adjust the open limit by turning the open limit screw with a flathead screwdriver. Turn the limit switch screw clockwise to increase the travel and counterclockwise to decrease the travel. Every full turn is a 3-inch adjustment. Adjust the limit in small increments.
Ask you helper to push the wall button again to close the garage door. The bottom of the door should seal to the floor without setting the safety force adjustment. The safety force is a safety mechanism that automatically stops the door and reverses the travel when the door hits an obstruction.
Adjust the down limit using the flathead screwdriver to turn the down limit screw. Turn it clockwise to close the door further or counterclockwise if the door is closing too tightly and setting off the safety force.
Operate the door up and down to check the limit adjustments. Continue adjusting as necessary.