Many timber front doors have two separate locks: a nightlatch higher up the door and a mortice lock below it. If one starts sticking or you want to replace both, choosing replacements involves more than matching the colour of the fittings.
What does each lock do?
A nightlatch usually latches when the door closes and can be opened with a key from outside. The way it opens from inside depends on the model. A mortice lock sits inside a pocket cut into the door. A mortice deadlock operates a bolt, while a mortice sashlock also has a latch operated by a handle.
Having two locks does not automatically mean the door meets a particular security standard. The lock models, their fitting, and the condition of the door and frame all matter.
Why a replacement may not be like for like
Older mortice locks can have unusual case dimensions or faceplates. A modern replacement might need a different keyhole position, a change to the existing recess, or an adjustment to the receiving plate in the frame. On some doors, a compatible replacement is preferable to the first lock that looks similar.
Before ordering a lock, a locksmith will normally check:
- Lock type: deadlock or sashlock, and whether a separate handle is needed.
- Case and backset: how far the keyhole or spindle sits from the door edge.
- Door and frame: timber condition, alignment, and how the bolt meets its keep.
- Existing openings: whether the new case, faceplate and keyhole line up neatly.
- Security and access: any insurance requirements and how occupants can leave safely.
Should you choose a higher-security mortice lock?
For some external timber doors, a lock certified to BS 3621 may be appropriate. Look for the standard marked on the actual lock rather than relying on a seller’s general description. Requirements vary by insurer and property, so check your policy before buying. If the door is used as an escape route, the way the lock opens from inside needs particular attention; a key-operated lock is not suitable in every situation.
A higher-security lock is only a useful upgrade if it fits correctly and the surrounding timber and keep are sound. Changing the lock alone will not repair a loose frame or damaged door.
What photos help with a quotation?
For an initial assessment, send a clear photo of the full door, a close-up of each lock from the inside, and a photo of the metal faceplate on the door edge. If you can safely see the maker’s name or model number, include that too. Do not remove a working lock from your only secure entrance just to take measurements.
When to arrange a repair rather than force the key
If the key needs excessive force, the bolt catches on the frame, or the door will not secure properly, stop forcing it. Repeated pressure can damage the key or mechanism. A locksmith can assess whether adjustment, repair or replacement makes more sense.
Locksmith Dundee Ltd provides lock repair and replacement services in Dundee and surrounding areas. See our door lock replacement service, request an appointment, or call 01382 671054. We can check whether your existing nightlatch and mortice lock can be replaced like for like or need a different fitting.