How to Fix a Door Lock That Won't Lock

A door lock that won't lock is a serious security problem. Whether the bolt won't extend, the key won't engage, or the latch won't catch, here's how to diagnose and fix it.

Why Won't My Door Lock?

• Bolt misaligned with strike plate: The bolt can't enter the strike plate hole
• Worn or broken lock mechanism: Internal parts have failed
• Door misalignment: The door has shifted so the bolt doesn't line up
• Strike plate hole too small or mispositioned: The bolt hits the plate face instead of entering
• Dry or seized mechanism: The bolt won't extend due to lack of lubrication
• Damaged bolt: The bolt itself is bent or broken

Step 1: Check Bolt-to-Strike Plate Alignment

Close the door and try to lock it. Watch where the bolt is trying to go. Apply chalk or lipstick to the bolt end, close the door, and engage the lock — the mark shows exactly where the bolt is hitting. If it's hitting above, below, or beside the hole, realign the strike plate.

Step 2: Reposition or Replace the Strike Plate

Loosen the strike plate screws and shift it in the direction needed. For small misalignments, use a metal file to enlarge the strike plate opening. For larger misalignments, fill the old screw holes and reposition the plate.

• Gator Door Strike Plate (Satin Nickel) — universal replacement with longer screws for stronger hold

Step 3: Lubricate the Lock Mechanism

If the bolt is stiff and won't extend fully, lubricate the mechanism.

• DuPont Silicone Lubricant — spray into the keyhole and bolt mechanism
• DuPont White Lithium Grease — for the bolt and strike plate contact surfaces

Step 4: Fix Door Alignment

If the door has shifted so the bolt can't reach the strike plate, fix the underlying alignment issue:

• Tighten loose hinges
• Add hinge shims to adjust door position
• Plane the door edge if swelling is pushing it out of alignment

• Door Hinge Shims 10-Pack — fine-tune door position without modifying the frame

Step 5: Replace the Lock Cylinder

If the key turns but the bolt doesn't extend, the internal mechanism is broken and needs replacement.

• Mortise/Rim Lock Single Cylinder Replacement — standard size, includes 5 keys
• CML Keyed Entry Door Knob Set — full replacement including knob and latch

Step 6: Replace the Latch

If the latch bolt is bent or broken, replace just the latch assembly.

• Door Latch Kit with Built-in Scoring & Chisel Tools — fits standard door thicknesses

Security Note

A door that won't lock is a security vulnerability. If you can't fix it immediately, use a door security bar or chain lock as a temporary measure while you source parts.