The key turns but the door will not open

Try this before anything else

With the key in the lock, push the door firmly towards the frame — or pull it towards you if it opens outwards — lift the handle very slightly to take the weight off the latch, and turn the key again. If it suddenly works, you have your answer: the lock is fine and the bolt is binding against the frame.

That is the situation nine times out of ten. Nothing inside the lock has failed. The door and the frame have simply stopped agreeing about where the hole is.

The one diagnostic that settles it

Open the door, hold it open, and work the lock.

• The bolt slides freely with the door open, but jams when closed. The lock is healthy. The problem is alignment: the strike, the hinges, the frame or the weatherstrip.
• The bolt is stiff or immovable even with the door open. The fault is inside the lock — worn pins, a failing cam, debris, or a cylinder screw done up so tight that it is binding the tailpiece.
• The key turns but nothing moves at all. Something has disconnected inside — a sheared tailpiece, a broken cam or a failed latch mechanism.

Do that test before you buy anything. People replace perfectly good locks for a problem that was living in the doorframe.

What is usually causing it

• Loose hinge screws. The commonest cause of all. Over years, the screws holding the top hinge work loose, the door sags at the latch edge, and the bolt no longer lines up with its hole.
• A swollen door or frame. Timber moves with humidity. A door that is fine in July can bind in February.
• A strike plate that has shifted — or one that was slightly wrong from the day it was fitted and has finally been found out.
• Paint build-up on the frame, the strike or the door edge.
• Compressed or swollen weatherstrip holding the door a few millimetres proud of where it should sit.
• A worn latch or deadbolt with rounded edges that no longer clears the strike cleanly.
• Over-tightened cylinder screws on the inside face of a deadbolt, squeezing the mechanism.
• House movement. Settlement shifts frames slowly and permanently, and doors are the first thing to notice.

Fixes you can reasonably do yourself

1. Tighten every hinge screw on both the door and the frame. Free, quick, and often the entire fix.
2. Lift a dropped door. Replace one screw in the top hinge on the frame side with a screw long enough to reach the structural stud behind the frame. As it tightens it draws the frame back and lifts the latch edge of the door. Go slowly and re-test after each turn.
3. Find the witness mark. Rub chalk, lipstick or a soft pencil on the end of the bolt, close the door and operate the lock. The mark left on the strike shows you exactly where the bolt is hitting and in which direction.
4. Clear the strike. Scrape off built-up paint and debris in and around the strike hole.
5. Back off the cylinder screws a quarter turn on the interior face of a deadbolt and re-test. If that frees it, they were over-tightened.
6. Use a dry lubricant in the cylinder and on the latch. Not oil, not general-purpose spray.

What not to do

• Do not keep forcing the key. Keys snap at the shoulder, and they snap without warning. You would then have a jammed door and a broken key inside the lock.
• Do not hit the handle or the door with anything. Bent spindles and split stiles are permanent; the misalignment was not.
• Do not oil the cylinder. It buys a week and costs a cylinder.
• Do not enlarge the strike hole with whatever is nearest. A hacked-out strike weakens exactly the part of the door that resists being forced. If the hole genuinely needs adjusting, it needs adjusting properly and often needs the plate repositioning instead.
• Do not remove the lock without noting orientation. Latches are handed, cams sit one way round, and a reassembled-backwards lock behaves like a broken one.
• Do not kick the door because it will not open. You will replace the frame, the strike and possibly the door for a fault that was three millimetres wide.

When to call somebody

• The bolt is stiff even with the door open — the fault is inside the lock.
• The key turns and nothing moves. Something has sheared.
• You are locked out or locked in right now.
• It is a multi-point lock, a mortise lock, an aluminium storefront door or a fire door. These are not places to experiment.
• Hinge tightening and strike cleaning have not fixed it, and the door is getting worse.
• You can see damage to the frame, or the door has been forced at some point.

What a locksmith will actually do

1. Run the door-open test first, to separate the lock from the frame.
2. Check the hinges, the reveal around the door and the swing, and lift a dropped door where that is the cause.
3. Mark the bolt to find precisely where it is fouling, and reposition or replace the strike rather than butchering the hole.
4. Service or replace the latch, the cam or the cylinder if the fault is inside the lock.
5. Fit a reinforced strike with screws long enough to reach the stud, if the frame needs it — which also makes the door significantly harder to force.
6. Close, lock, unlock and re-test the door through its full swing with you standing there.