Why will my night latch not hold the door shut?
The snib that has been left in the wrong position, the staple that has moved, the worn latch spring and the connecting bar that has slipped — in the order to check them.
- Difficulty
- beginner
- Time
- 25 min
- Read
- 4 min
Short answer
Check the snib first: a night latch held back on the snib will not latch at all and that accounts for most cases. Then look at whether the latch bolt is meeting the staple squarely. If the bolt springs out weakly or sticks, the case needs oiling or the spring has gone and the latch needs replacing.
Night latches are simple and they fail in a small number of predictable ways. Two of them are not faults at all — the snib and a door that has dropped — and both are free to fix, so they are worth ruling out before buying anything.
Step by step
- Check the snib.The small button or lever on the case. On most models it can hold the latch withdrawn so the door does not latch at all. If somebody has flicked it while the door was open, the symptom is exactly a latch that has stopped working. Push it back and try.
- Watch the bolt as the door closes.Open the door and hold it a few centimetres from closed. Push it slowly and watch the latch bolt meet the staple. It should ride up the sloped face and drop into the aperture. If it hits the edge of the staple, or the face below the aperture, the door has dropped or the staple has moved.
- Adjust the staple, not the latch.If the bolt lands low, the staple can usually be moved down a few millimetres. That means new screw holes; fill the old ones with glued dowel or matchsticks rather than screwing into a loose hole. If it has to move more than a few millimetres, sort the door's hinges instead.
- Test the latch action off the door.With the door open, push the latch bolt in with a finger and let go. It should spring out sharply. Sluggish return means a dry case; no return means a broken spring.
- Oil the case.A few drops of light machine oil where the latch bolt enters the case, then work it thirty or forty times. A latch that has been painted around, or that lives on an exposed door, dries out and this is often the whole fault.
- Check the deadlocking pin.Automatic deadlocking latches have a small secondary pin beside the main bolt. It must rest on the face of the staple when the door is shut, not drop into the aperture with the bolt. If the staple is a fraction out of position the latch will hold but will not deadlock, which is a real security loss.
- Check the connecting bar engagement.If the key turns but does not withdraw the latch, the flat bar from the cylinder is no longer engaging the mechanism. Take the case off and look — a bar cut a shade too short, or a cylinder that has rotated, produces this exactly.
- Check the cylinder fixing screws.The two long screws through the door work loose over years. A cylinder that turns bodily in the door rather than the key turning in the cylinder is a loose fixing, and it will eventually shear the bar.
- Replace the latch if the case is worn.Night latches are inexpensive and are not economic to repair. If the spring has gone or the case is corroded, fit a new one — and take the opportunity to fit an automatic deadlocking model if the old one was not.
If it doesn't work
Door has to be pulled hard to latch
Cause: The bolt is dragging on the staple, usually because the door has dropped or the frame has swollen — Fix: Look for the rub mark on the staple. Adjust the door at the hinges if it has dropped; move the staple a fraction if it has not.
Latch holds but the door rattles
Cause: The staple is set too far out, so the bolt is not pulling the door against the stop — Fix: Move the staple in by a millimetre or two, or fit a staple with an adjustable tongue. Do not cure it with a draught strip alone.
Key turns freely and does nothing
Cause: The connecting bar has slipped, sheared, or the cylinder has rotated — Fix: Remove the case and inspect. A sheared bar is usually a symptom of a loose cylinder, so fix the fixing as well as the bar.
The knob turns but the latch does not move
Cause: Broken internal linkage in the case — Fix: Replace the latch. This is not a repairable part.
Questions people ask
Can I stop the door latching without using the snib?
Not sensibly. That is exactly what the snib is for. If the snib is broken, that is a reason to replace the latch.
Should the snib be left on at night?
On a deadlocking model, leaving the latch deadlocked out means it cannot be slipped, but it also means anyone inside must operate the snib to open the door. On a final exit door, think about escape before adopting that as a habit.
Why does my latch work in summer and not in winter?
The door and frame move with moisture. A latch that is marginal in one season fails in the other, which means the staple position or the door alignment is on the edge and should be corrected properly.