Doorknobs occasionally stick because of changes in temperature and humidity levels. Such problems may improve somewhat when those conditions change again. Other sticking problems are caused by wear and tear. The latch may fail to retract when the knob is turned, or fail to return when the knob is released. When a doorknob mechanism sticks, it can make it hard to open a door, or it may prevent a person from obtaining privacy. Fixing a stuck doorknob can be as easy as applying some lubrication, but it sometimes requires replacement.
Jiggle the doorknob in an attempt to jar loose the stuck part. Though a simple fix, the problem may be that the springs are not being properly engaged or the latch is failing to retract/extend.
Spray the doorknob mechanism with lubricant and turn the knob a few times to help spread the lubricant. Inspect the mechanism on both sides for rust. If rust is present, remove it with a wire brush, and spray lubricant on the mechanism to keep it working properly.
Check the latch. If the latch is retracted and the door knob will not turn, the latch may be misaligned and caught on something. Place a flathead screwdriver just above the latch, and tap it with a hammer. Repeat on the underside of the latch to attempt to free it.
Inspect the doorknob assembly more closely. Remove the screws from the plate and remove the doorknob from the door. Look inside the doorknob for obstructions or breaks in the mechanism. Remove any obstructions from the assembly with needle-nose pliers. Replace the doorknob if the assembly is broken.