When replacing a door lock, the useful starting point is the door you have, the part that needs changing and the security requirements for your home. A timber door with a mortice lock needs a different approach from a uPVC door with a multipoint mechanism.
This guide explains the main lock types and the checks to make before arranging a replacement. Your insurance policy, the door’s condition and safe escape from the property all matter. There is no single lock that suits every home.
Start with the reason for replacing the lock
Common reasons include moving into a new home, losing keys, damage, an unreliable lock or a security upgrade. If somebody may still have a key, changing the relevant lock or cylinder lets you control who can enter. If the door is difficult to close or the handle will not lift, ask for the cause to be checked rather than assuming a new cylinder will fix it.
Mortice locks on timber doors
A mortice lock sits within the edge of the door. A mortice deadlock has a locking bolt; a mortice sashlock combines a bolt with a latch. Both need a replacement that suits the existing door and fitting.
For security, look for independently tested products. Where your insurer requires BS3621, check for the British Standard Kitemark and the standard number on the lock faceplate. Five levers alone do not prove that a mortice lock meets BS3621. Confirm the exact wording in your policy rather than relying on a product described only as “insurance approved”.
Nightlatches and rim cylinders
A nightlatch is fitted on the inside surface of the door and commonly pulls shut behind you. Its rim cylinder is the part operated by a key from outside. Depending on the problem, replacing that cylinder may be enough; a damaged or unsuitable nightlatch may need a wider change.
Do not assume that a basic latch provides the same protection as a tested locking system. A locksmith can check whether it needs a suitable additional lock and whether the arrangement meets your policy.
Euro cylinders on uPVC and composite doors
Many uPVC and composite doors use a euro cylinder within a multipoint lock. The cylinder operates the mechanism, while the multipoint system secures the door at several points. Changing the cylinder and replacing the whole multipoint mechanism are different jobs.
For resistance to lock snapping, the Master Locksmiths Association describes three routes: a Sold Secure SS312 Diamond cylinder, a TS007 three-star cylinder, or a TS007 one-star cylinder combined with two-star protective door furniture. Check the product’s actual certification, not only an “anti-snap” marketing claim. Correct sizing and fitting matter too.
Multipoint mechanisms
If a door will not lock smoothly, the cylinder may not be the only issue. The mechanism, handle or door alignment may need attention. Arrange an assessment before buying a complete replacement. Keep the replacement compatible with the door and its existing security specification.
Safe escape and doors to flats
Security must not prevent people from getting out safely. The MLA notes that flats, apartments and homes with a single exit have different escape requirements from other homes. A lock that needs a key to open from inside is not automatically the right choice for every entrance.
Have the correct escape arrangement checked, particularly for a flat entrance or fire door. Do not choose a lock from a security rating alone: the door, building and means of escape must be considered together.
What to check before accepting a quote
- Which part needs replacing: cylinder, lock case, nightlatch or complete mechanism?
- What exact product and security certification are included?
- Does the proposed lock meet your insurer’s stated requirements?
- Is it suitable for the door and safe escape from the property?
- Does the total include parts, labour, call-out charges and VAT where applicable?
- How many keys are included, and what warranty covers the work?
Ask for a clear total before the work starts. A cheap cylinder-only quote is not comparable with a complete mechanism replacement. There is no reliable fixed price without knowing the door, lock and fault.
Frequently asked questions
Do I need to replace every lock after moving house?
Replacing the relevant locks or cylinders is a way to make sure old keys no longer give access. Review all external access points and ask which parts need changing, rather than assuming every complete mechanism must be replaced.
Is every five-lever lock BS3621 certified?
No. Check for the Kitemark and BS3621 marking. The number of levers alone is not enough.
Will a new cylinder fix a stiff uPVC door?
Not necessarily. The door and locking mechanism need checking so the actual cause is addressed.
Can I choose by brand alone?
Choose by compatibility, independently tested security, insurance requirements and safe escape. A familiar brand name does not answer all of those questions.
Further reading
Guidance used for this article: the Master Locksmiths Association’s door lock types guide, BS3621 guide and lock-snapping protection guide.