How to Repair Door Locks

Door locks are complex mechanisms with lots of tiny moving parts and, as such, can malfunction on occasion. Here we look at how to fix typical door lock problems. For problems with door knobs and locksets, please see Repairing Door Knobs & Hardware.

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If your door key doesn’t work right, the first and most obvious step is to be sure you’re using the right key. Once you get the door open, try the key again. If it works easily, the deadbolt isn’t engaging the strike plate properly. If it doesn’t work any easier, lubricate and clean the lock. Otherwise, coat the key with graphite and work it back and forth in the cylinder several times.

If the key turns but doesn’t unlock the lock, disassemble the lock so that you can be sure the cam or tang is properly engaged with the bolt. Replace any broken parts and reassemble the lock.

If the key won’t go into the lock, ask yourself if the weather is cold enough for the lock to be frozen. If it is, hold the key with a heavy glove and heat, then work it gradually into the keyway. Repeat heating and inserting the key until the ice has melted.

A new key that won’t go in or work properly may have rough spots that need to be filed off. To find them, hold the key over a candle to blacken it with soot and then turn it very slightly in the lock and remove it. File down any shiny areas where the soot was removed by the rough spots.

Door Lock Works Slowly

Exterior locks can freeze, interior locks get dirty, and small internal parts eventually wear out or break. Before you buy a replacement lock, try some quick remedies:

Put some graphite into the keyhole, either by squeezing it from a tube or dusting it onto a key, and then operate the lock a few times to work the graphite into the mechanism. Lock de-icers contain alcohol and other lubricants that help to dissolve gummy, dirty deposits. The last resort is to disassemble the lock to see if something has jammed or is broken—you may be able to set it straight or replace the part without buying a whole new lock.

Entire Lock Cylinder Turns

A cylinder turns when the setscrew(s) meant to hold it in place become loose or broken.

Mortise lockset: Remove the faceplate (if there is one) at the door’s edge and locate the one or two cylinder setscrews. They should be in line with the center of the cylinder. Tighten the setscrew(s) by turning clockwise—be sure they engage the slot that runs along the edge of the cylinder (the key slot should be perfectly vertical). Replace the faceplate.

Surface-mounted rim lock: Unscrew and remove the cover, called a “case.” Tighten the cylinder setscrews. Replace the case.

Lock Doesn’t Latch Properly

When a door latch doesn’t click into position, it usually means the latch and the strike plate are out of alignment. Tighten the hinge screws and then try adjusting the strike plate by loosening its screws and shifting it slightly.

When possible, it’s easier to file the slot in the strike plate a little bit so that it will receive the latch. Shifting the strike plate’s position usually involves mortising the jamb, filling part of the old mortise, and so forth. You can also solve misalignment by replacing the strike plate with an adjustable strike plate.

A latch can stick for many reasons, most of which are easily fixed. Check that the hinge screws are tight. If the door is out of alignment, the latch will bind. Also check the knob and lock assembly for loose screws or misalignment. Finally, look closely at the strike on the door jamb—if it’s blocked or out of adjustment, the latch won’t run freely in and out.

Deadbolt Is Stuck

The chances are good that the bolt is having a hard time finding the throat in the strike plate. Be sure the strike plate is secure and in reasonable alignment with the bolt. You can file the edges of the strike plate a little, and even slightly round the edges of the deadbolt’s end. If this doesn’t work, you’ll probably have to remove the strike plate, fill the screw holes with glue and wood matchsticks, trim flush with the jamb, reposition the strike plate properly, and screw it back in place.

Key Is Broken Off in Lock

Using pliers, try to grip and pull the key straight out. If you can’t get a grip even with needle-nose pliers, cut off a coping saw blade and, with the teeth pointed outward, insert the blade into the keyway and try to hook and drag the key out. As a last resort, remove the lock cylinder. Insert a stiff wire into the cam slot at the back of the cylinder and push the key out. Or take the cylinder to a locksmith.

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