Why does my key turn but the door will not unlock?

A key that turns freely and achieves nothing has lost the connection between the cylinder and the bolt. Where that connection has broken decides whether this is a ten-pound part or a locksmith.

Safety

What you'll need

• The key
• A screwdriver
• A torch
• PTFE or graphite lock lubricant

Step by step

1. Open the door and repeat the test.This single check splits the problem in two. Working with the door open means an alignment problem; failing with the door open means the lock itself.
2. Feel what the key is doing.A key that spins with no resistance at all has lost its cam. A key that turns against resistance and stops has a jammed or broken mechanism further in.
3. Check the cylinder is not loose.On a euro cylinder there is one long screw through the lock forend. If it has backed out, the cylinder rotates in the lock body instead of driving the cam.
4. Look at the cam through the keyway.With the cylinder out, the cam is the small metal tab at the back. If it has sheared or the securing screw has fallen out, the cylinder turns and nothing follows.
5. Test the mechanism without the cylinder.With the cylinder removed, operate the lock with a screwdriver in the cam slot. If the bolts move freely, the cylinder is at fault. If they do not, the lock body has failed.
6. Lubricate before condemning anything.A dry cylinder full of dust can slip past its pins. A puff of PTFE or graphite lock lubricant, worked in with the key, fixes a surprising proportion of vague cylinder faults.
7. Never use oil or WD-40 in a lock.Light oils attract dust and gum the pins over months, and displace the dry lubricant the lock was built with. Locks want dry PTFE or graphite.
8. Check the door alignment if it only fails when closed.The bolts are being held by the strike or the keeps under load. Lift the handle and try again — if it works when lifted, the door has dropped.
9. Replace the cylinder if it is the cylinder.A euro cylinder is measured from the fixing screw to each end and swaps out in five minutes. Take the chance to fit an anti-snap cylinder while it is out.
10. Call a locksmith for a failed gearbox on a locked door.If the mechanism has failed with the door locked, opening it usually means drilling. That is a job worth paying for rather than damaging the door.

Tips

• Test both keys. A worn key that has lost its shoulders can turn a cylinder partially and feel exactly like a failing lock.
• If the key has felt gradually gritty for weeks, the lock has been telling you it is failing. Replace it before it strands you.
• Keep a spare cylinder if you have a uPVC door. They are inexpensive, and the failure always comes at an inconvenient moment.

Common mistakes

• Spraying oil into the keyway — Oil holds every particle of dust that enters the lock and turns to a paste. A lock that was merely dry becomes a lock that is seized, and the residue is very hard to flush out.
• Forcing the key harder when it starts to resist — Keys are brass or nickel silver and are designed to be weaker than the cylinder. Applying force snaps the blade off inside the keyway, which almost always means drilling the lock out.

If it doesn't work

Questions people ask