Lock won't turn: causes and solutions

The key goes into the cylinder, but it won't turn anymore — or only halfway, and only if you force it. This is one of the calls we get most often, and almost always at the worst possible moment: in the morning as you're heading out to work, or in the evening as you're getting home. The good news: a lock that's starting to resist usually warns you weeks ahead, and with the right diagnosis it can often be repaired without replacing everything. This guide helps you understand what's going on — and above all how to avoid the one move that snaps the key off in the cylinder.

First, a simple test: door open or door shut?

This is THE diagnostic reflex every locksmith reaches for first. If you can get the door open, try locking it with the door open:

• The key turns normally with the door open — the cylinder is healthy. The problem is one of alignment: the bolt can no longer find the strike plate because the door has dropped on its hinges or the wood has swollen. It's mechanical, not a lock fault.
• The key resists even with the door open — the problem is in the cylinder itself: worn pins, a clogged mechanism, or a misshapen key.

This one test changes everything: adjusting a strike plate or a set of hinges has nothing to do with replacing a cylinder.

The most common causes

The cylinder is worn or clogged

A cylinder is a precision mechanism: pins calibrated to a tenth of a millimetre. Over the years, dust, pocket grime and the wear on the brass all create play. The key catches now and then at first, then more and more often. If your lock is more than ten years old and the resistance has crept up gradually, this is suspect number one.

It's the key that's worn, not the lock

Try another copy of the key if you have one, ideally a spare that hasn't seen much use. A key that lives in your pocket wears out faster than the cylinder: its teeth round off and no longer lift the pins properly. If the spare turns perfectly, there's no need to touch the lock at all — just cut a fresh key from the good copy.

The door has dropped or swollen

Very common in older Brussels townhouses with their heavy doors: the hinges work loose, the door drops a few millimetres, and the bolt scrapes against the strike plate. Autumn damp also swells wooden doors — that's the classic November call. The telltale sign: lifting the door slightly by the handle while you turn the key makes it lock more easily.

Frost

On an exposed door (a garage entrance, a garden gate), moisture condensed inside the cylinder can freeze on a cold night. If the problem turned up on a winter morning and concerns an outside door, gently warm the key (hot water, a lighter — the key, not the cylinder) before trying again.

The moves to avoid at all costs

• Never force it with both hands. A key that snaps inside a seized cylinder turns a simple repair into a broken-key extraction — and often a full replacement.
• No cooking oil and no greasy spray such as ordinary WD-40: the greasy film traps dust and clogs the mechanism within weeks. If you want to lubricate, use graphite powder or a dry PTFE lubricant only, both made for cylinders.
• Don't take the cylinder apart yourself if the door is shut: on a locked door it's impossible without proper tools anyway, and the attempts leave marks that make a clean opening harder.

Repair or replace?

If the problem is alignment, a locksmith adjusts the strike plate or the hinges — the cylinder doesn't get replaced. If the cylinder is at fault, replacement is usually the lasting solution: a clean-out buys a worn mechanism a few more months, rarely more. It's also the moment to move up to a better-quality cylinder, or even a security key protected by an ownership card if you've lost track of how many copies are out there. Our lock replacement service comes out the same day across the Brussels region.

And if the lock has finally seized up completely with the door shut? That's a classic emergency: see our jammed lock page — we're available around the clock.