This traditional sliding patio door it’s not locking because the door is out of alignment. One of the will Runner sets has collapsed causing the door to be tilted in the frame. The edge of the door has four mushroom bolts which move up and down in unison when the small lever behind the handle is pushed up or down. If working correctly the lever should not be able to go up and down when the door is in the open position. On the edge of the door is a small extended push catch which is pressed in when the door is closed. This releases the mechanism allowing the small lever behind the handle to be pushed up and down to engage the mushroom bolts and lock the door. Once the wheels are replaced the door will be put back in and realigned so that when closing the push button can be pressed and so allowing the door to be locked.