Sometimes when the door locks are bun or tight, people often like to put some lubricating oil into the lock eyes. In this way, the door locks may be smooth, but because the oil is easy to stick, it will be in the lock eyes later. It is easy to accumulate dust slowly and form oil putty, which makes the door lock more prone to failure. The correct solution: cut some pencil pieces or some candle pieces, blow them into the inside of the lock cylinder through the thin tube, and then insert the key repeatedly for several times. In some cases, due to the gravity of the door leaf, or the cause of the door leaf, the door leaf sinks, and the door is locked or the door is not smooth. At this time, it is often difficult to open the door with a key and lock the door. At this time, do not forcibly twist the key, so as not to break the key and increase trouble. The correct solution: you should first check the reason. If the door leaf sinks due to loose leaf, the loose leaf should be fastened with screws. If the door frame is deformed or its cause is unrecoverable, start with the door frame and expand the lock tongue accordingly, so that the door lock switch door can resume normal and smooth.