Fulham Locksmith Service Team
Local locksmith team
15 Jul 2026 4 min read
Your front door takes a knock, a key snaps in the lock, or you have just moved into a flat on Fulham Road and want to know who else might have a key — and suddenly you are facing a question most people have never had to think about before: do you need to swap just the cylinder, or does the whole lock mechanism need replacing? Getting this right matters, because the wrong choice either leaves a security gap or costs you more work than the job needed. This guide walks through exactly how to tell the difference, what each option actually involves, and when to call a professional locksmith London team rather than attempting anything yourself.
The answer turns on the type of lock you have, the nature of the problem, and sometimes a measurement or two. Whether you have a euro cylinder in a uPVC door, a 5-lever mortice deadlock on a Victorian timber door in Parsons Green, or a Yale-type nightlatch on a communal flat entrance, the logic is the same: change the smallest part that solves the problem properly.
Frequently asked questions
Do you need to change the cylinder a new lock when you move into a property in London?+
In the UK, the most practical approach when moving into a new home or flat is to have the cylinders replaced rather than changed over in a more complex way. For euro cylinders — which are standard on uPVC and composite doors — a full cylinder swap is quicker, often cheaper in terms of parts, and gives you a known-provenance unit that may be a higher security rating than whatever was fitted before. For 5-lever mortice locks, a locksmith can re-lever the mechanism to match a new key set, but this is more involved. Either way, yes — changing access when you move in is strongly recommended, and many letting agents and housing associations are legally or contractually required to arrange it between tenancies.
How do you measure a backset on a mortice lock, and why does it matter?+
The backset is the distance from the face edge of the door to the centre of the keyhole (or spindle hole for the handle). To measure it, hold a tape measure against the door edge and measure horizontally to the middle of the existing keyhole. On UK timber doors, 44mm and 57mm are the two most common sizes. It matters because if a replacement lock case or cylinder has the wrong backset, the bolt will not align with the keep in the door frame and the door will not lock. Always confirm this measurement before ordering a replacement part, or let your locksmith measure it on the job.
How do you change a combination lock code if you have lost the instructions?+
The reset procedure varies by make and model, but on most mechanical combination locks it involves aligning the dials to the current working code, using a change key or shifting an internal reset tab, setting the new code, then releasing and testing. On electronic keypad locks, there is usually a programming mode accessed via a hidden reset button and the existing master code. Without the instructions, the safest step is to find the model number on the lock body and search the manufacturer's website, or call a professional locksmith who can often identify the unit and guide you through it. Attempting to force the mechanism is very likely to damage it beyond economic repair.
What is the difference between a cylinder replacement and a full door lock replacement London job, and how do I know which I need?+
A cylinder replacement swaps only the barrel that the key turns — it leaves the lock case, gearbox, or body completely untouched. This solves problems like lost keys, unwanted keyholders, a snapped or drilled cylinder, or a worn barrel. A full door lock replacement is needed when the mechanism itself has failed: the gearbox on a uPVC door is cracked, the levers in a mortice lock are worn or damaged, the lock body was forced during a break-in, or the existing lock does not meet the security standard your insurer requires (such as BS3621). A good way to tell: if the door locks and unlocks correctly but you just want to change who holds a key, a cylinder is probably all you need. If the mechanism feels wrong — stiff bolts, hooks not engaging, the handle feeling loose or dead — the mechanism itself needs attention. When in doubt, call 020 7871 7823 and describe the symptoms; we can usually give you a good steer before anyone comes out.
