Sticky locks and stuck locks can happen for a variety of reasons, including gunk and buildup inside the lock, age of the lock, and broken pieces of an old key trapped inside the lock. Locks can also stick when the key to the lock is a badly made duplicate. These tips will help you fix these problem as they arise.
If the key to your lock was newly made from an original, the key could simply be a bad duplicate. Feel the edges of the key for pieces of scratchy metal. If the edge of your key is rough, run it along a stiff wire brush or gently rub it with sand paper until the edges of the key feel smooth. If this doesn't help, take the key back to the person who made it along with the original key. Ask for a new duplicate.
If you're having trouble sticking your key in the lock at all, a broken key could be the cause. Use a key extractor kit to remove the broken part. Key extractor tools are long and slender and have ends shaped like tiny hooks. These tools are designed to fit in the space in between the key and the lock.
Slip the key extractor inside the lock so that the bottom of the hook can slip underneath the jagged edge of the broken key. Once the hook finds purchase, pull the broken key and extractor out together.
As locks age, grime can build up inside the lock and inside the internal parts of the door handle. This buildup of gunk and dirt can cause the entire door handle to seize up when it's being turned. The best way to fix this problem is to spray the inside of the door handle and lock with graphite. Graphite can reduce friction inside the lock and door handle, enabling better functionality and operation.
To do this, start by spraying the inside of the lock with commercial graphite. If the door handle continues to freeze up, use a screw driver to remove the screws that connect the two sides of the handle. Take the entire piece off the door, then spray the insides of the door handle with graphite. Once this is done, put the handle back on.
If the door handle is still sticking, seek out locksmith services such as Advance Lock & Key. A professional locksmith will be able to fix the lock on a more permanent basis, or will be able to replace the lock altogether.