In short:
- Most sliding doors lock with hooks in the door's edge that catch a keeper on the frame. If the two don't line up, the door won't lock, even though the lock itself may be fine.
- The usual reasons are a door that isn't fully closed, a keeper that has shifted, or a panel sitting lower or higher because of worn rollers or a dirty track.
- Check which control you're using: on many locks a snib only latches, and the key deadlocks.
- Don't lift the panel off its track or force the handle. A stuck heavy glass panel is a two-person job at the very least.
- Until it's fixed, keep any security gate across the opening locked, or lay a bar in the bottom track as a stopgap.
How a sliding door lock works
A hinged door has a bolt that shoots straight out into the frame. A sliding door can't work that way, because the panel moves sideways. Instead, most sliding door locks have one or more hooks (some makers call them beaks) that swing out of the edge of the door and hook behind a keeper, also called a strike, fixed to the frame. When the hooks are behind the keeper, the panel can't slide open.
Many locks have two controls on the inside: a snib (a small lever or button) and a key. ASSA ABLOY's instructions for its Endeavour sliding door lock sum up a common arrangement in four words: "snib to latch, key to deadlock". The snib holds the door shut; the key locks it so the hooks can't simply be released. If you only ever use the snib, the door may be latched but not deadlocked.
That alignment is why so many sliding doors stop locking with nothing actually broken. ASSA ABLOY's fitting instructions have the installer close the door and move the keeper up or down until it's central to the handle before tightening it. Anything that later changes the door's height or closing position undoes that.
Symptoms and likely causes
| What happens | Likely cause | Safe first step |
|---|---|---|
| Snib or key moves, but the door still slides open | Hook missing the keeper: panel not fully closed, keeper shifted or panel height changed | Close the door firmly against the frame and try again; look for scrape marks on the keeper |
| Snib or key won't move unless you push or lift the door | Hook binding on the edge of the keeper | Note which way you have to push; it tells the technician which way things have shifted |
| Door won't close fully into the frame | Debris in the bottom track, a damaged track or worn rollers | Clean the track (see below) |
| Door rumbles or drags when it slides | Worn or broken rollers, or grit in the track | Clean the track; if it's still rough, the rollers may need attention |
| Snib flops loosely, nothing engages | Broken part inside the lock | Stop and call for a repair or a new lock |
| Key won't turn, or turns without effect | Cylinder fault, wrong key, or a broken link between cylinder and lock | Check it's the right key; don't force it |
| Hooks stick out while the door is open and catch the frame | Lock left in the locked position, or a fault | Return the snib or key to unlocked before closing; don't slam the door on extended hooks |
Safe checks you can do
- Close it properly. Slide the door all the way into the frame and hold it there while you work the snib or key. Some sliding locks also have an anti-slam feature (ASSA ABLOY's Endeavour has an anti-slam pin), and on locks like this the hooks may not work as intended unless the door is fully home.
- Use the right control. Try the key as well as the snib, if there is one. Make sure you're turning it the right way.
- Look at the keeper. Shiny scrape marks above or below the opening show where the hooks are landing. A keeper with loose or missing screws has probably moved.
- Look at the gap. With the door closed, is the gap between the door and the frame even from top to bottom? A wedge-shaped gap suggests the panel is no longer sitting square.
- Clean the bottom track. Stegbar, an aluminium window and door maker, recommends vacuuming tracks regularly and using a light dry silicone spray on them about once a year. It also warns never to use solvent-based cleaners or highly abrasive materials on aluminium frames. Small stones, leaves and pet hair in the track are enough to lift a panel.
- Check the maker's guidance before putting anything into the lock itself. Advice on lock lubricants differs between makers, and the wrong product can gum up a mechanism.
If cleaning the track and closing the door firmly sorts it, keep an eye on it: the underlying wear is often still there. If you've found a loose keeper, an uneven gap or a lock that's broken inside, that's the point to call.
What makes it worse
- Lifting the panel off its track. Large glass panels are very heavy and can fall when they come free, and some doors have anti-lift blocks that are there for security. Leave panel removal to someone with help and the right method.
- Forcing the snib or key while the hook is jammed against the keeper. That's how the small parts inside break.
- Slamming the door to get it to catch, or slamming it with the hooks sticking out.
- Bending the keeper with pliers to make it "catch". It may lock once and then not at all, and it weakens the keeper.
- Solvents and scouring pads on aluminium frames and tracks.
Keeping the house secure tonight
A sliding door that won't lock is an open door, and patio and back doors are often out of sight from the street. Until it's fixed:
- Lock any security gate or trellis across the opening, if there's one in front of the sliding door.
- Lay a bar in the bottom track. A length of wood or metal cut to fit between the sliding panel and the frame stops the panel from sliding open. It's a stopgap, not a lock, and only works from inside.
- Close curtains or blinds so it isn't obvious the door is a weak point.
- If the door was damaged in a break-in, see securing doors and gates after a burglary.
Repair, adjust or replace?
Many sliding door locking problems are adjustments: moving the keeper, correcting the panel height or dealing with the track. When the lock has broken inside, the lock body usually needs replacing; lock shapes and sizes vary, so matching a replacement to the door's frame profile matters. Your options will be explained on site.
- Lock repair covers adjusting keepers and repairing locks that are otherwise sound.
- Lock replacement covers fitting a new lock when the old one is broken, worn out or no longer secure enough.
If a broken roller or a badly damaged track is the root cause, that part of the job may be for an aluminium door specialist. The technician will tell you if so. For other locks in the house, our guide to euro cylinders and anti-snap upgrades explains what to look for in a cylinder.
What to tell us when you call
- The door type: aluminium or timber, and how many sliding panels.
- Photos of the lock on both sides, the keeper on the frame, and the gap between door and frame with the door closed.
- What happens when you use the snib and the key, and whether pushing or lifting the door changes anything.
- Any brand name on the lock or handle.
- Whether the door can be secured another way tonight, so we know how urgent it is.
We're a mobile locksmith in Roodepoort and work 24/7. The call-out fee is R250, the technician quotes on site before any work starts, and payment is by EFT, cash or card.
Questions
Why did my sliding door lock fine for years and then stop?
Usually because something gradually changed the door's position: rollers wearing down, grit in the track or a keeper working loose. The lock itself may be fine.
Can I spray lubricant into the sliding door lock?
Only if the lock or door maker says so, and with the product they recommend. Makers' advice differs, and the wrong spray can collect dust and stiffen the mechanism.
Is a track bar enough on its own?
It stops the panel sliding, which helps as a stopgap, but it's not a substitute for a working lock. Get the lock sorted as soon as you can.
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 Roodepoort, so we come to your door.
Sources and further reading
- ASSA ABLOY: Endeavour sliding door lock installation instructions — Hook (beak) lock for sliding aluminium and timber doors; snib to latch, key to deadlock; anti-slam pin; strike adjusted up or down until central to the handle
- Stegbar: Maintaining aluminium windows and doors — Vacuum tracks regularly; light dry silicone spray on tracks yearly; keep tracks and drain holes clear; no solvent-based or abrasive cleaners on aluminium