Something is wrong with your lock. Before calling for help—or before attempting repair yourself—accurate diagnosis saves time, money, and frustration.
This guide walks you through identifying common lock problems so you understand what you’re dealing with.
The Two Essential Tests
Before anything else, perform these tests:
Test 1: Door Open vs Door Closed
With the door standing open:
- Does the key turn smoothly?
- Does the handle operate normally?
- Do the bolts extend and retract?
Compare to door closed operation.
| Door Open | Door Closed | Diagnosis |
|---|---|---|
| Works fine | Difficult | Alignment/frame issue |
| Difficult | Difficult | Lock mechanism issue |
| Works fine | Works fine | Intermittent—investigate further |
Test 2: Different Keys
Try a spare key that’s rarely used:
| Spare Key | Daily Key | Diagnosis |
|---|---|---|
| Works | Doesn’t work | Worn daily key |
| Doesn’t work | Doesn’t work | Lock mechanism issue |
| Works better | Works poorly | Key wear contributing |
"These two tests take 30 seconds and immediately narrow the problem. Skip them, and you may fix the wrong thing.
Symptom-Based Diagnosis
Find your symptom below:
Key Won’t Insert at All
Possible causes:
- Wrong key (check carefully)
- Debris in keyway
- Frozen mechanism (cold weather)
- Vandalism/foreign object inserted
Quick check: Look into the keyway with a torch. Is there visible obstruction?
Likely solution: Debris removal or thawing. If obstruction is deliberate, professional extraction needed.
Key Inserts But Won’t Turn
Possible causes:
- Wrong key
- Worn key not engaging pins
- Frozen mechanism
- Seized/corroded internals
- Cylinder failure
Quick check: Try spare key. Try with door open. Check for ice in cold weather.
Likely solution: If spare key works, cut new daily key. If nothing works, lubrication or cylinder replacement.
Key Turns But Lock Doesn’t Operate
Possible causes:
- Broken cam (connection between cylinder and mechanism)
- Stripped gearbox (multipoint locks)
- Disconnected tailbar
Quick check: Can you feel resistance when turning, or does it spin freely?
Likely solution: Professional repair. The cylinder-to-mechanism connection has failed.
Lock Works But Door Won’t Open
Possible causes:
- Bolts not fully retracting
- Frame has shifted
- Secondary lock engaged
- Door swollen (weather)
Quick check: With door “unlocked,” can you see the bolt still in the frame? Does lifting the door help?
Likely solution: Alignment adjustment or frame work. Often fixable without lock replacement.
Handle Feels Loose or Floppy
Possible causes:
- Loose handle screws
- Worn spindle
- Broken internal spring
- Gearbox wear (multipoint)
Quick check: Does tightening visible screws help? Does the handle return to position when released?
Likely solution: Often simple tightening. If spring failure, handle or gearbox repair.
Lock Is Stiff to Operate
Possible causes:
- Lack of lubrication
- Debris accumulation
- Worn mechanism
- Misalignment adding friction
Quick check: Stiff with door open or only closed? Responds to lubrication?
Likely solution: Proper lubrication often resolves stiffness. Persistent stiffness indicates wear.
Lock Makes Unusual Sounds
| Sound | Likely Cause |
|---|---|
| Grinding | Metal-on-metal friction, worn parts |
| Clicking (new) | Something broken loose inside |
| Scraping | Misalignment, mechanism catching |
| Nothing (too quiet) | Springs may have failed |
Intermittent Problems
Lock works sometimes but not others:
Possible causes:
- Worn components at tolerance limits
- Temperature/humidity effects
- Alignment that’s borderline
- Failing springs
Quick check: Is there a pattern? Time of day? Weather conditions? After heavy use?
Likely solution: Worn locks with intermittent problems typically get worse. Plan for repair/replacement.
Lock Type Considerations
Euro Cylinders (uPVC/Composite Doors)
Common issues:
- Cylinder wear → Replace cylinder (relatively simple)
- Gearbox failure → Mechanism repair needed
- Cam breakage → Cylinder replacement
Most euro cylinder problems are solved by cylinder replacement, which is straightforward and affordable.
Mortice Locks (Wooden Doors)
Common issues:
- Lever wear → May be serviceable
- Spring failure → Usually requires lock replacement
- Key wear → New key may work
Traditional mortice locks can sometimes be repaired rather than replaced.
Multipoint Locks
Common issues:
- Gearbox failure → Expensive but replaceable
- Individual hook/bolt failure → Component replacement possible
- Handle mechanism → Usually handle replacement
Multipoint locks have more components that can fail individually.
What Information Helps a Locksmith
When you call, provide:
- Door type: uPVC, composite, wooden, internal
- Lock type: If known (euro cylinder, mortice, multipoint)
- Exact symptom: What isn’t working
- Test results: Door open vs closed, spare key results
- Recent changes: Weather, damage, new sounds
- Urgency: Locked out? Security concern? Convenience issue?
This information helps the locksmith arrive prepared, potentially reducing time and cost.
"“My lock doesn’t work” requires investigation. “My euro cylinder turns freely but doesn’t operate the gearbox” gets the right parts brought first time.
When Diagnosis Points to Replacement
Some diagnostic results indicate replacement rather than repair:
- Very worn mechanism: Repair may not be cost-effective
- Old lock lacking security features: Upgrade opportunity
- Repeated problems: Fundamental issues won’t stop
- Attack damage: Even repaired, security may be compromised
See our guide on repair vs replace decisions for detailed guidance.
Frequently Asked Questions
How do I know if the problem is my lock or my door?
If the lock operates smoothly when the door is open but not when closed, it's likely a door/frame alignment issue. If the lock is stiff regardless, it's the lock mechanism itself.
Why does my lock only work sometimes?
Intermittent problems usually indicate worn internal components. Pins or springs that are degraded work unpredictably. Temperature and humidity changes can also cause intermittent issues.
Can I diagnose the problem myself before calling?
Yes, and it helps. Try your lock with the door open, test with a spare key, note when problems occur. This information helps a locksmith arrive prepared with the right parts.
What does it mean if my key turns but nothing happens?
The connection between the cylinder and lock mechanism has failed. On multipoint locks, this often means the gearbox or cam is broken. Professional repair is needed.
Why is my lock making grinding noises?
Grinding indicates metal-on-metal friction from lack of lubrication or worn components. Try graphite lubricant first. If grinding persists, internal parts may be damaged.
Should I keep using a problematic lock?
A lock that's difficult to operate is also a security weakness. Worn mechanisms are easier to pick or manipulate. Address problems promptly.
Why does my lock work with one key but not another?
Keys wear at different rates depending on use. Your daily key may be worn while a spare works perfectly. Try a spare before assuming the lock is faulty.
Is a stiff lock a security risk as well as an inconvenience?
Yes. Difficulty locking often means difficulty locking reliably—you may leave thinking you're secured when you're not. Plus, worn mechanisms can be easier for criminals to manipulate.
Take Action
Next time your lock misbehaves:
- Pause before forcing anything
- Test with door open vs closed
- Try a spare key if available
- Match symptoms to this guide
- Communicate findings when seeking help
Five minutes of diagnosis can save hours of complication. If the problem persists, consider whether signs indicate your lock needs replacing.