The test that tells you where the problem is
Open the door and turn the deadbolt. If it throws and retracts smoothly with the door open, the lock is fine and the door is the problem. If it is stiff even with the door open, the lock itself needs attention; see sticky door lock.
Why the bolt and the strike stop lining up
- Sagging hinges. Over time the weight of the door pulls the top hinge away from the frame and the door drops a few millimeters on the lock side.
- Seasonal movement. Wood doors and frames swell and shrink with the weather. A door that was fine in winter can bind in a hot summer.
- The house settling. In older homes the frame itself moves a little over the years.
- A strike plate that was never quite right, often after a new lock was fitted to an old hole.
Fixes you can try
- Tighten the hinges. Start with the top hinge. If the screws spin, replace one screw in the top hinge with a long screw that reaches the wall framing behind the jamb; it often pulls the door back into line on its own.
- Find where the bolt hits. Rub a little lipstick or chalk on the end of the bolt, close the door and turn the key. The mark on the strike shows which way it is off.
- Adjust the strike. For a millimeter or two, the strike hole can be filed slightly larger; for more, the strike plate is moved.
Smart locks feel it first
A motorized smart lock has far less force than a hand on a key, so a slightly misaligned door that you never noticed will make a smart lock jam, report an error, or drain its batteries quickly. If your smart lock keeps failing to lock, check the door alignment before blaming the lock. See smart lock dead battery and smart lock installation.
When it is a locksmith job
If the hinges are tight and the strike is right and the bolt still binds, or the lock itself is stiff with the door open, it is time for a lock repair or a new deadbolt installation. A deadbolt that only half throws is not doing its job, so it is worth fixing soon.
Questions people ask
Why does my deadbolt only lock with the door open?
Because the bolt and the strike plate no longer line up when the door is closed. Usually the door has sagged on its hinges or moved with the weather.
How do I fix a deadbolt that does not line up?
Tighten the hinges, putting a long screw into the top hinge if needed, then check where the bolt hits and adjust or move the strike plate.
My smart lock keeps jamming. Is the lock broken?
Often not. Smart locks have little force, so a small misalignment that a key would push through makes them jam. Check the door first.
Is a half-locked deadbolt safe?
No. A bolt that does not throw fully can be forced much more easily, so get the alignment fixed soon.