Why your key sticks — and why it usually is not the lock

The usual causes

• Door or frame movement, so the latch is dragging on the strike plate.
• A worn copy of a copy of a key, cut further from the original each time.
• Grit inside the cylinder, common on street-facing doors.
• Oil-based lubricant applied previously, which attracts dust and gums up.

What you can check safely

Open the door and turn the key with the door swung clear of the frame. If it turns easily like that, the lock is fine and the alignment is the problem. If it is stiff either way, the cylinder or the key is worn.

Lubrication

Use a dry graphite or PTFE-based lock lubricant, sparingly. Avoid general-purpose oil sprays in cylinders — they work for a week and cause problems for years.

When to call

If a key needs force, if it has begun to bend, or if the lock sometimes fails to throw fully, get it looked at. A repair or a fresh key cut to code is a small job; extracting a snapped key and replacing a cylinder after hours is not.