A lock turning but not locking usually means the key turns the cylinder, but a failed cam or a misaligned door stops the bolt from throwing. The cylinder is doing its job; the part that drives the bolt is not. Do not force the key.
This is a frustrating fault, because the lock feels like it is working while the door stays unsecured. The cause is nearly always the cam inside the cylinder, the multipoint mechanism, or the door alignment. This guide helps you tell which it is, explains your repair options, and shows when the job needs a locksmith.
Why won’t the bolt engage when I turn the key?
The bolt will not engage when the key turns but the part that should drive the bolt has failed or is blocked. The common causes are a worn or broken cam, a failed uPVC gearbox, a stripped connection inside the cylinder, or a dropped door stopping the bolt reaching the keep.
A cam is the small arm at the centre or end of the cylinder that the key turns to drive the bolt or the multipoint mechanism. When the cam wears, snaps, or loses its grip on the bolt, the key spins or turns freely while nothing locks. On a uPVC door, the same fault often sits in the gearbox that the cylinder drives.
| Symptom | Likely cause |
| Key turns freely, no resistance | Worn or broken cam, or stripped connection |
| Key turns, hooks or bolt do not move | Failed uPVC gearbox |
| Bolt throws part way, then stops | Misaligned door or worn mechanism |
| Locks only when you lift the handle hard | Dropped door straining the mechanism |
| Thumbturn spins without locking | Worn cam or internal fault |
Matching your symptom to the table shows whether the cylinder, the mechanism, or the door is at fault.
Is it the cylinder, the mechanism, or the door?
You can narrow it down in a minute. If the key spins with no resistance, the cam or cylinder has failed. If the key meets resistance but the bolt will not throw fully, the door is misaligned or the mechanism is binding. Test the lock with the door open to rule the door in or out.
A door lock cylinder reads the key and drives the bolt through the cam. If you turn the key and feel nothing, that link has broken, and the cylinder needs replacing. If you feel the bolt start to move but it jams before it locks, the bolt is catching on the keep or the frame, which points to a dropped door.
On uPVC and composite doors, lift the handle to engage the locking points before turning the key. If the handle will not lift or lifts but nothing locks, the gearbox has likely failed. Knowing which part is at fault decides your repair.
“When a lock turns but will not lock, the first thing we check is whether the key has any resistance,” says a Kingdom Locksmith locksmith. “No resistance means the cam has gone. Resistance with a bolt that will not throw usually means the door has dropped and the bolt is catching.”
What are the repair options?
Your repair options depend on the part that has failed. A worn cylinder or cam is replaced, a failed uPVC gearbox is swapped for a new mechanism, and a misaligned door is realigned. Most of these are quick, affordable jobs once the faulty part is identified.
For a spinning cylinder, replacement is the fix, because the cam cannot be repaired inside the barrel. When you replace it, fitting an anti-snap, TS007 3-star cylinder improves security at the same time. For a uPVC door, a new gearbox or full multipoint strip restores the locking points. For a misaligned door, hinge and keep adjustments bring the bolt back into line.
| Fault | Repair | Typical UK cost (guide) |
| Worn or broken cylinder cam | New euro cylinder | £15–£60 part, plus labour |
| Failed uPVC gearbox | Gearbox or mechanism replacement | from £100 plus parts |
| Misaligned or dropped door | Hinge and keep adjustment | from £80–£96 labour |
| Locksmith labour, standard hours | – | £65–£96 per hour |
| Emergency or out-of-hours call-out | – | £85–£200 |
These are guide prices and vary by lock type, location, and time of day, so ask before work starts. Because a door that will not lock is a security risk, a fast door won’t lock fix can diagnose the cam, gearbox, or alignment and secure the door the same day.
When should you call a locksmith?
Call a locksmith straight away if the door will not lock and you cannot secure it, the key spins with no resistance, or you are about to leave the property. An unlockable door is an open invitation, and forcing the mechanism risks turning a small repair into a full replacement.
A lock turning but not locking is one of the few faults you should treat as urgent, because the door cannot be left secure overnight. The Master Locksmiths Association recommends using an approved, vetted locksmith, who can identify the failed part and replace it without damaging the door. Acting quickly keeps both your home and the repair bill under control.
Frequently asked questions
Question: Why does my key turn but the door won’t lock?
Answer: The key is turning the cylinder, but the cam that drives the bolt has failed, or the door has dropped so the bolt cannot throw. No resistance points to the cam; resistance with a jammed bolt points to alignment.
Question: Why does my lock spin without locking?
Answer: A spinning cylinder means the cam or the internal connection has broken, so the key no longer drives the bolt. The cylinder cannot be repaired and needs replacing.
Question: My uPVC door handle lifts but won’t lock, what is wrong?
Answer: The gearbox inside the multipoint mechanism has likely failed. Lifting the handle should engage the hooks, and a broken gearbox stops that. It needs a mechanism replacement.
Question: Is a door that won’t lock a security risk?
Answer: Yes. An unlockable door cannot be secured, so treat it as urgent. Get it repaired the same day, and consider an anti-snap cylinder upgrade when the part is replaced.
Question: Can I fix a lock that turns but won’t lock myself?
Answer: You can check and adjust a dropped door, but a failed cam or gearbox needs a replacement part fitted correctly. Forcing the key only causes more damage.
Securing a door that turns but won’t lock
A lock turning but not locking nearly always comes down to a failed cam, a broken gearbox, or a dropped door, and identifying the right one is half the job. Acting fast matters, because a door that will not lock leaves your home open every minute it stays unfixed. At Kingdom Locksmith, we diagnose spinning cylinders, replace worn cams and uPVC gearboxes, and realign dropped doors for homes and businesses across the UK, often securing the door on the first visit. Do not leave a door you cannot lock. If your lock turns but will not lock, get a fast door won’t lock fix and make your home secure again.