Why will my sliding patio door not lock?
Separating a sash that has dropped from hook bolts that have moved and keeps that have loosened — and why a sliding door's lock is far more sensitive to height than a hinged door's.
- Difficulty
- beginner
- Time
- 40 min
- Read
- 3 min
- Safety
- caution
Short answer
Check whether it locks when you push the sash hard against the closing stile. If it does, the sash is not travelling far enough or the seal is holding it off. If not, look at the hook bolts against their keeps — a sash that has settled by a couple of millimetres puts the hooks below the keep slots.
Sliding patio doors lock with hook bolts on the closing stile that swing into keeps in the frame or in the fixed leaf. Because the sash rides on adjustable rollers, its height is not fixed, and a very small change in roller height or a very small amount of roller wear moves every hook relative to every keep. That is why this fault appears gradually and then suddenly.
Safety
Step by step
- Try locking it with the sash pushed hard home.Push the sash firmly against the closing stile with your shoulder and turn the handle at the same time. If it locks that way, the door is not closing fully — a stiff track, a compressed seal or an obstruction is holding it a few millimetres short.
- Look at the hook against the keep.Throw the hooks with the door open a hand's width, then close it slowly and watch. The hook should swing into the mouth of the keep. If it arrives below the slot and meets solid metal, the sash has dropped.
- Use chalk if you cannot see.Rub chalk or a smear of grease on the leading face of each hook, close and try the handle, then open and look at where the mark transferred to the keep. It shows the direction and roughly the amount.
- Raise the sash if it has dropped.Wind both roller adjusters up equally, a quarter turn at a time, checking the lock after each. Keep an eye on the slide as well — you are looking for the point where it both slides freely and locks.
- Check the keeps if the height is right.Keeps are screwed into the frame and can loosen or be knocked out of position, particularly at the bottom. Check the screws and, on adjustable keeps, whether somebody has previously wound them out to compensate for something else.
- Clean the hook bolts and the keeps.Salt, dust and old grease build up in the keeps of a patio door. Clean both, then a dry PTFE spray. A hook that cannot fully enter a dirty keep produces exactly this symptom.
- Check the handle and the drive.If the handle turns freely with no resistance and the hooks do not move at all, the lock's internal drive has failed and the lock needs replacing. If the handle is stiff and the hooks move partway, it is more likely to be alignment.
- Check the sash is square.Look at the gap where the closing stile meets the frame. If it is tapered, the top and bottom hooks are at different distances from their keeps and one will always be wrong. Square the sash at the rollers before anything else.
- Fit a temporary secondary lock if you cannot fix it today.A track bar, a patio door jammer or a proprietary sash stop makes the door secure overnight. It is not a substitute for the repair but it is far better than an unlocked door.
If it doesn't work
Locks in summer, not in winter
Cause: The seal and the frame move with temperature, and the setting is marginal — Fix: Re-set the height so it locks comfortably in both seasons rather than perfectly in one. If it is genuinely marginal, worn rollers are usually the underlying reason.
Handle turns fully but nothing engages
Cause: Failed lock drive, or a disconnected drive rod — Fix: Take the handle off and look at whether the spindle is turning the mechanism. A sheared drive means a new lock; a disconnected rod can sometimes be re-engaged.
Only the top hook engages
Cause: The sash is out of square, or the bottom keep has moved — Fix: Square the sash at the rollers first. If it is square and the bottom hook still misses, the bottom keep has shifted and needs repositioning.
Locks but the door still rattles
Cause: The keeps are set too far out, so the hook engages without pulling the sash tight — Fix: Adjust the keeps in a millimetre at a time until the seal is compressed and the handle still turns without a fight.