Door Locks When Open but Not When Closed: Causes

In short:

If the bolt, latch or hooks move freely with the door open, the lock mechanism is probably fine. The problem is where the bolt meets the frame.
Common causes are a door that has dropped on its hinges, a strike plate or keep that has moved, timber that has swollen, a door expanding in the heat, or a sliding door that has dropped on its rollers.
Forcing the key, or lifting and shoving the door every day, wears the lock and can snap a key or leave the bolt jammed in the frame.
The fix is usually adjustment, not a new lock. Leave hinge and keep adjustments to a professional unless you have the maker's instructions and know what you're doing.

What this symptom tells you

It's a frustrating fault, but it's also a helpful one. Lock makers test locks with the door open precisely so the frame isn't involved: EVVA's cylinder manual says the locking function must be checked while holding the door open. If your lock passes that test, smooth with the door open and stiff or blocked when it's closed, the lock is doing its job. Something stops the bolt, latch or hooks from going into the frame.

You may notice one or more of these:

The key turns freely with the door open, but stops part-way or needs real force once the door is shut.
The door only locks if you push it hard against the frame, pull it towards you, or lift it by the handle.
On a multipoint door, the handle won't lift fully when the door is closed, but lifts easily when it's open.
The latch doesn't catch, and the door swings open again unless you slam it.
On a sliding door, the hook won't swing into the keeper, or the lock lever stops part-way.
It's worse at certain times: hot afternoons, after rain, or in one season.

If the lock is also stiff with the door open, the cause is more likely inside the lock. See why a door lock goes stiff instead.

What's going on: the bolt and the strike plate

When a door locks, its bolt (or latch, hooks or rollers) goes into an opening in a metal plate on the frame, called the strike plate or keep. There's only a small margin around it. If the door sits even a few millimetres lower, higher, further in or further out than it did when the lock was fitted, the bolt meets the edge of the plate instead of the opening.

Illustration The lock side of a door seen from inside (schematic, not to scale). In A, the bolt lines up with the opening in the strike plate. In B, the door has dropped, so the bolt meets the edge of the plate. With the door open, the lock works normally. With the door closed, the bolt binds or can't go in.

The same idea applies to every lock type. A multipoint lock has several keeps instead of one, so it's even more sensitive. ERA's fitting guide for one of its multipoint locks tells installers to check that the centre of the latches lines up with the centre of the rollers on the keeps. It also specifies a consistent 3–4mm gap between the door edge and the frame, and warns that above 4mm part of the lock won't meet its keep and the door won't close correctly.

Why doors and frames move out of line

The door has dropped. Hinges wear, and hinge screws work loose or lose their grip in timber. The door sags on the lock side, so the bolt sits lower than the opening. The MLA (the UK locksmiths' trade association) lists dropped doors and worn or faulty hinges among the causes of sticking locks.
The strike plate or keep has moved. Loose screws, a damaged frame, or a plate refitted slightly out of position after earlier work.
Timber has swollen or shrunk. Wooden doors and frames take up moisture and dry out again, which changes how the door sits.
Heat expansion. The MLA notes that uPVC expands and contracts with temperature, and Everest, a UK door company, says hot weather and direct sun can make a door expand. A door that gets strong afternoon sun may lock in the morning and not in the late afternoon.
Seals and frames. New, thicker or swollen weather seals can push the door away from the frame. Damaged or distorted frames also put load on the lock. ASSA ABLOY's South African care guide notes that faulty hinges, warped doors and distorted frames put excessive load on other components and shorten their life.
Obstruction. Paint, grit or a loose screw head in the strike opening or keep can stop the bolt going fully home.
Sliding doors off level. A sliding door that has dropped on its rollers, or has grit in its track, sits lower or doesn't close fully. Everest's advice is that the door has to slide freely into place to lock correctly, with the rollers adjusted so the lock lines up with the keep.

How it shows up on different locks

Locks when open, not when closed: what you notice and what usually needs attention
Lock type	What you notice	What usually needs attention
Lever mortice lock (timber door)	Key tightens at the end of the turn; bolt only goes in if you push or lift the door	Strike plate position, hinge wear or loose hinge screws, swollen timber
Cylinder lock in a mortice case	Key turns freely with door open, stops part-way when closed	Strike plate alignment; the load can also strain the cylinder and its cam
Multipoint lock	Handle won't lift fully when the door is shut; you have to push the door in hard first	Keep positions, door-to-frame gap, hinge adjustment, compressed or swollen seals
Rim nightlatch	Latch doesn't catch in the staple, or deadlocking doesn't engage	Staple position on the frame, door drop
Sliding-door hook lock	Hook won't swing into the keeper, or lever stops part-way	Roller height, debris in the track, keeper position

If you're not sure which type you have, our guide to mortice, cylinder and multipoint locks explains the differences.

Safe checks you can do

These checks involve looking, not adjusting. Don't remove screws or move parts.

Confirm the pattern. With the door open and unable to swing shut, lock and unlock it a couple of times. Then try with the door closed. Smooth open and stiff closed confirms an alignment problem.
Look at the gaps. With the door closed, look at the gap between the door and the frame on the lock side and along the top. An uneven gap, wide at the top of the lock side and tight at the bottom, suggests the door has dropped.
Look for scrape marks on the strike plate or keeps and on the bolt itself. Bright metal or worn paint shows where they rub, and so which way the door has moved.
Try the chalk mark test, gently. With the door open, rub a little chalk or lipstick on the tip of the bolt and draw the bolt back in. Close the door, turn the key only until you feel resistance, then turn it back, open the door and look at where the mark has landed on the strike plate. Don't push past the resistance.
Look into the strike opening. Loose grit, paint flakes or other debris can be brushed out with a soft brush.
Look at the hinges for missing or loose-looking screws, or a hinge that has pulled away from the timber.
On a sliding door, look along the track for grit or stones, which can be swept or vacuumed out, and see whether the door sits level in its frame.
Note when it happens: the time of day, sun on the door, recent rain, or any recent work on the door such as painting or new seals.

What to avoid

Forcing the key. The bolt is pressing against the strike, so extra force goes into the key and the cylinder. Winkhaus warns that its keys and cylinders aren't suitable for transmitting high frictional forces. This is how keys snap. If one does, see what not to do with a broken key.
Lifting and shoving the door every day as a workaround. It loads the mechanism each time, and one day the bolt may jam half-way into the frame, leaving the door stuck shut or unlockable.
Filing or chiselling the strike plate to make the opening bigger. It weakens the frame, can let the door rattle, and doesn't correct the movement.
Moving the strike plate or keeps yourself. New screw holes next to old ones in timber hold poorly. The MLA advises against realigning a door yourself, because it can involve taking parts of the lock apart or removing hinges.
Spraying lubricant. It won't fix misalignment. Where lubrication is due, follow the lock maker's guidance, because makers specify different products.
Leaving the door unlocked or relying only on a slide bolt because locking is a struggle.

When to call, and what helps the technician

Call a locksmith once you need to push, lift or force the door to lock it, or if the key has started to bend. Caught early, this is usually an adjustment, not a new lock. A lock repair visit typically checks the door-open behaviour, the strike or keep alignment, the hinges and the door gap, then adjusts what has moved. If the frame is split, the door is badly warped or the timber has swollen a lot, a carpenter or door installer may also be needed, and the technician will say so. As a mobile locksmith in Sandton, we can see the door, frame and lock together on site, which is where this kind of fault has to be judged.

Photos and details that help:

The lock from both sides, and the door edge showing the faceplate and any brand name.
The strike plate or keeps on the frame, close enough to show scrape marks.
The whole door, closed, showing the gaps at the top and on the lock side.
The hinges, and for a sliding door, the track and the bottom of the door.
When it started, whether it changes with time of day or weather, and any recent work on the door.

Questions

Why does my door lock fine in the morning but not in the afternoon?

The door and frame are probably expanding in the heat, especially if the door gets direct sun. If the bolt or hooks only just clear the strike or keeps, a small amount of expansion is enough to make them bind. It's an alignment problem that a technician can usually adjust out.

Is this a locksmith job or a carpentry job?

Often a locksmith job: adjusting the strike plate or keeps, and checking hinges. It becomes a carpentry or door-installer job when the frame is damaged, the door is badly warped, or the timber needs planing or re-hanging. A technician can tell you which it is once they've seen the door.

Do I need a new lock?

Usually not, if you deal with it early. But if the door has been forced shut for months, the cylinder, cam or gearbox may have worn. In that case a part, or occasionally the lock, may need replacing as well as the alignment being corrected.

Need a locksmith to look at it?

If this hasn't solved the problem, our lock repairs service covers it. We're a mobile locksmith in Sandton, so we come to your door.

Sources and further reading

ERA: Touchkey multipoint lock installation guide — 3–4mm door-to-frame gap, latches centred on keep rollers, keep adjustment, resistance signals incorrect fitting
EVVA: lock cylinder installation and operating manual — Check the locking function with the door held open
Master Locksmiths Association: uPVC door lock mechanism sticking — Weather, dropped doors and worn hinges; don't realign a door yourself
Everest: patio doors that will not lock — Sliding doors must slide freely; roller adjustment so locks line up with keeps; heat expansion
ASSA ABLOY South Africa: Product Care and Maintenance — Faulty hinges, warped doors and distorted frames overload other components
Winkhaus: profile cylinder fitting and care instructions — Keys and cylinders aren't designed to transmit high frictional forces; door jamming can distort the cylinder
RACV: how to maintain your locks — Needing to lift or push a door to lock it, and strike-plate wear, as signs of misalignment