Why this is urgent
A commercial door that will not lock means the building is not secured. Most commercial insurance policies require all locks to be in good working order; a documented faulty lock can void cover for any break-in that follows. Until repair, the building should be alarmed, monitored, or have alternative locking in place (e.g. internal padlock on a secondary point).
The good news: the underlying fault is almost always one of four things, and same-day repair is realistic.
The two-minute diagnostic test
Stand at the door. Push it firmly closed with your hand. While holding it closed, try to turn the key.
If the lock engages when held closed but will not engage when the door is released, the closer is not bringing the door fully home — closer fault or pivot misalignment. The lock and strike are fine.
If the lock will not engage even when the door is held firmly closed, the fault is in the lock body, the cylinder, or the strike plate. The closer is innocent.
This single test resolves the diagnosis in two minutes. Everything else flows from the result.
Cause 1: closer not bringing the door fully home
If the door is stopping 5–10 mm short of the strike, the lock literally cannot engage — the bolt has nowhere to go. Causes: closer is set too soft (latch-speed valve wound back too far), closer is leaking and losing pressure, pivot is worn and the door is dropping, or the door is dragging on the threshold and being slowed.
Field-fix order: first, adjust the closer latch-speed valve to give the door more force in the last 15 degrees. Test. If that doesn’t resolve it, check pivot wear (rock the top of the door — any play and the pivot is worn). If pivot is sound and closer adjustment didn’t work, the closer is end-of-life and needs replacement.
Cause 2: strike plate misaligned
The bolt is extending but missing the strike, or hitting the strike face and bouncing back instead of engaging. Common after door drops, frame settlement, or attempted forced entry that has pushed the strike out of position.
Field-fix: identify where the bolt is meeting the strike (mark with a pencil after operating the lock with door open). Either re-position the strike, or replace it with a new one positioned to meet the bolt cleanly. 30–60 minutes typically.
Cause 3: hookbolt or lock body wear
The lock turns, the bolt moves, but it does not extend its full distance or it sticks. Internal wear in the lock body — broken spring, worn lift cam, or sticking spindle.
There is no field-repair for internal lock body wear. The lock body is replaced as a unit — typically 30–90 minutes including refitting the cylinder and checking the strike alignment.
Cause 4: cylinder failure
The key turns loosely, the key won’t go in fully, or the key has broken in the cylinder. The lock body may be fine; the cylinder is end-of-life.
Cylinder replacement is the fastest of all lock repairs — typically 5–15 minutes for a standard Euro profile cylinder. Same-day in almost all cases.
After a cylinder replacement, the old keys no longer work — new keys are issued with the new cylinder. This is also the moment to consider upgrading to anti-snap, anti-bump cylinders if the door is on a security-critical opening.
What to do in the next hour
Practical steps if a commercial door has just failed to lock:
- Secure the building by other means — internal padlock on an alternative point, alarm system armed, building monitored.
- Call your commercial door contractor and describe the symptom. The two-minute test above narrows the diagnosis.
- Take a photograph of the lock from inside and outside, and a short video showing the door closing and the lock not engaging.
- For high-security premises (cash, pharmacy, jewellery), arrange overnight security cover if the engineer cannot attend before close of trade.
Permanent fix and prevention
The permanent fix is one of: closer adjustment, closer replacement, pivot replacement, strike re-position or replacement, lock body replacement, or cylinder replacement. Diagnosis defines which.
Prevention is twofold. First, maintain the closer — most lock failures actually start as closer failures (door stops short, lock can’t engage). A six-monthly closer adjustment prevents most. Second, replace cylinders and lock bodies before they fail — typically 10 years on a Euro cylinder, 5–15 years on a commercial lock body depending on cycle count.