Introduction

Door locks rarely fail without warning. Most develop small faults over time, such as a stiff key, a handle that doesn't return properly or a lock that only works when the door is open.

These early symptoms often indicate wear elsewhere in the door system rather than complete lock failure. A dropped door, worn gearbox, poor alignment or ageing cylinder can all produce similar symptoms, making accurate diagnosis essential before replacing parts.

This A–Z guide explains the most common lock faults, what they mean, their most likely causes and links to our in-depth guides covering repairs, maintenance and security.

Common Lock Symptoms

Not sure what's wrong? Start with one of these common problems.

• Lock won't turn unless lifted
• Key difficult to remove
• Key only turns halfway
• Lock feels stiff
• Door won't lock
• Door won't unlock
• Key snapped in the lock
• Lock works with the door open
• Handle won't lift
• Easier to lock with door open
• Lock jams occasionally

A

Alignment Problems

Symptoms

• Handle difficult to lift
• Key stiff
• Lock only works with the door open

Common Causes

• Door dropped
• Hinge wear
• Building movement

Usually repairable through professional door realignment.

Complete Guide

➡ Complete Guide to Door Alignment & Lock Performance

Anti-Snap Lock Damage

Modern anti-snap cylinders are designed to resist one of the most common burglary methods used against Euro cylinders.

Complete Guide

➡ Complete Guide to Euro Cylinder Door Locks

Related Articles

• Do Anti-Snap Locks Really Work?
• What Makes a Lock Snap Resistant?

B

Broken Gearbox

The centre gearbox has failed internally.

Symptoms

• Handle loose
• Door won't unlock
• Key turns but nothing happens

Often repairable by replacing the gearbox rather than the complete locking mechanism.

Complete Guide

➡ Complete Guide to Multipoint Locking Systems

C

Cylinder Failure

The Euro cylinder has worn internally.

Symptoms

• Key difficult to insert
• Key sticks
• Key won't turn

Usually solved by replacing the cylinder.

Complete Guide

➡ Complete Guide to Euro Cylinder Door Locks

D

Dropped Handle

The handle no longer springs back correctly.

Symptoms

• Lever hangs down
• Poor latch operation

Usually Caused By

• Broken spring cassette
• Door misalignment
• Worn handles

Complete Guide

➡ Complete Guide to uPVC & Composite Door Handles

E

Excessive Force Required

A healthy door should operate smoothly.

If excessive force is needed there is usually another underlying fault rather than a worn lock alone.

Possible causes include poor alignment, worn mechanisms or increased compression.

F

Failed Centre Case

The centre case houses the gearbox and forms the heart of the multipoint locking system.

Wear here can prevent the entire mechanism operating correctly.

Complete Guide

➡ A to Z of door problems and trouble shooting.

 

G

Gearbox Wear

One of the most common causes of multipoint lock failure.

Symptoms

• Clicking
• Stiff operation
• Handle won't lift

Complete Guide

➡ Complete Guide to door problems explained.

H

Handle Spring Failure

The return springs inside the handles have broken.

Usually requires replacement handles.

Complete Guide

➡ Can a stiff handle cause lock failures?

I

Incorrect Adjustment

Poor hinge adjustment causes locking problems that are often mistaken for lock failure.

Complete Guide

➡ Complete Guide to Door Alignment & Lock Performance

J

Jammed Mechanism

Internal components have seized.

Possible Causes

• Broken gearbox
• Bent locking points
• Corrosion

Complete Guide

➡ Complete Guide to Multipoint Locking Systems

K

Key Will Not Turn

Possible Causes

• Door alignment
• Failed cylinder
• Broken gearbox
• Dirt inside the lock
• Lack of lubrication

Complete Guide

➡ Complete Guide to Euro Cylinder Door Locks

L

Loose Handles

Usually Caused By

• Loose fixing screws
• Worn backplates
• Broken fixing threads

Complete Guide

➡ Complete Guide to uPVC & Composite Door Handles

M

Misaligned Locking Points

Hooks or rollers no longer enter their keeps correctly.

Usually Caused By

• Door movement
• Hinge wear

Complete Guide

➡ Complete Guide to Door Alignment & Lock Performance

N

Noisy Lock

Symptoms

• Grinding
• Clicking
• Scraping

Usually indicates:

• Lack of lubrication
• Alignment issues
• Internal wear

O

Obsolete Mechanism

Replacement parts may no longer be manufactured.

Experienced locksmiths can often source:

• Genuine old stock
• Compatible alternatives
• Replacement gearboxes

P

Poor Compression

The door no longer seals tightly against the frame.

Symptoms

• Draughts
• Door movement
• Rattling

Usually indicates adjustment is required.

Q

Quiet Clicking

Often an early warning sign.

May indicate:

• Worn gearbox
• Handle spring wear
• Locking point wear

R

Roller Wear

Compression rollers no longer operate smoothly.

Symptoms

• Difficult locking
• Poor weather sealing

S

Sticking Lock

One of the most common homeowner complaints.

Possible Causes

• Door alignment
• Dirt
• Worn cylinder
• Failed gearbox

T

Tight Handle

The handle requires more effort than before.

Usually indicates:

• Door misalignment
• Increased compression
• Gearbox wear

U

Uneven Lock Engagement

Some hooks engage before others.

Usually caused by poor door alignment.

V

Vertical Door Movement

The door has dropped.

Common Symptom

• Lock difficult to operate

W

Worn Latch

The latch no longer retracts smoothly.

Symptoms

• Door won't close
• Door won't latch

X

eXcessive Wear

General wear affecting multiple components.

Usually found on locking mechanisms over 15–20 years old.

Y

Yellowed Lubricant Build-Up

Old grease hardens over time.

Can cause:

• Stiff operation
• Dirt build-up
• Increased wear

Cleaning and re-lubricating may restore smoother operation.

Z

Zero Engagement

The locking points no longer enter the keeps correctly.

Usually caused by:

• Severe door movement
• Failed hinges
• Incorrect adjustment

The door may appear locked while providing very little real security.

Most Lock Faults Are Repairable

Many homeowners assume a faulty lock means replacing the entire mechanism or even the whole door. In reality, most problems develop gradually and are often caused by alignment issues, worn handles, tired gearboxes or ageing cylinders rather than complete lock failure.

Identifying the underlying cause early can prevent unnecessary damage, extend the life of the locking system and often result in a much more cost-effective repair.

For more detailed information, continue to our complete guides covering door problems, door alignment, multipoint locking systems, Euro cylinders, door handles and home security.