A sliding glass door won't lock for one of three reasons: the mortise lock mechanism has worn out or seized, the handle is broken, or the door has dropped on worn rollers so the latch no longer lines up with the strike. Replacing the lock or handle fixes the first two; servicing the rollers to raise the door back into alignment fixes the third.
The three main causes
- Worn or seized mortise lock — the internal mechanism no longer throws the latch
- Broken or loose handle — it spins or won't engage the lock
- Misalignment — the door dropped on worn rollers, so the hook misses the strike
The alignment culprit people miss
Very often the lock itself is fine — the door has simply sunk because the rollers are worn, dropping the latch below the strike plate. Servicing or replacing the rollers raises the door back to where the latch meets the strike, and the lock works again. This is why a 'lock problem' sometimes turns out to be a roller problem.
What you can check safely
- See whether the latch lines up with the strike when the door is closed
- Check if the handle feels loose or spins freely
- Look for a door that visibly rubs the sill (a sign it has dropped)
The fix
We replace worn mortise locks and handles with quality hardware and correct any misalignment by servicing the rollers, so the door latches reliably. Ask us about added security too — see how to make a sliding glass door more secure.