If key is stiff or sticks while turning in lock cylinder.
Most people forget that locks like machines require periodic maintenance.
A simple spray lubricant such as WD-40 or fine machine oil will free up most locks. If key turns in lock but will not remove in the key out position. If deadbolt or key in knob lock is difficult to lock or unlock. A. Check to make sure alignment of bolt or latch fits strike plates without binding. If key turns in lock but bolt or latch does not retract.