| Summary: Changing a door lock is a manageable DIY job that boosts security after a break-in, a lost key, or moving house. This guide covers choosing the right lock, the tools you need, a step-by-step method, common mistakes, and when to call a professional locksmith. Most jobs take under an hour. |
Most of us don’t think about our locks until something goes wrong. A key goes missing on a night out, a tenant moves on, or worse, someone tries the door in the middle of the night. Swapping the lock is one of the quickest, cheapest ways to feel safe in your own home again.
It’s worth changing your lock when:
- You’ve just moved into a new home and have no idea who holds spare keys
- Keys have been lost or stolen
- There’s been a burglary or an attempted break-in
- The lock is stiff, worn or sticking
- Your insurer has asked for an upgrade
If you’re nodding at any of these, read on how to replace a door lock. It’s easier than you might think.
Work Out What Type Of Lock You Have
Before you buy anything, take a good look at your door. Getting this bit right saves a lot of faff later.
- Euro cylinder lock: the most common type on uPVC, composite and many timber doors. You’ll see a keyhole with a small cylinder fixed by a single screw in the edge of the door.
- Mortice lock: a rectangular lock set inside the door itself, usually found on older timber doors.
- Multipoint lock: found on uPVC doors, these lock at several points along the frame when you lift the handle.
For most homes, you’ll simply be swapping a euro cylinder, which is the easiest of the lot. That’s what we’ll walk through below.
Choose A Lock That Meets British Standards
Not all locks are equal, and the cheapest one on the shelf is rarely the best idea. Look for these markers:
- BS3621: Many insurers require it, so check your policy.
- TS007 3-star (or 1-star plus 2-star security handles): the rating to look for on euro cylinders. It means the lock is built to resist snapping, drilling, bumping and picking.
Anti-snap cylinders matter because snapping is a favourite trick among burglars. It’s the one upgrade we’d urge you not to skip.
What You’ll Need
Thankfully, there’s no need for a van full of kit.
- A new lock of the correct size
- A screwdriver (usually Phillips or flathead)
- A tape measure or ruler
- A bit of lubricant, such as graphite powder or a PTFE spray
Before you start, measure your existing cylinder. Take the measurement from the centre of the fixing screw to each end, outside and inside, and write both numbers down. Cylinders are sold in sizes like 40/40 or 35/45, and a lock that’s too long leaves part of it sticking out of the door, which makes it far easier to attack. Ideally, no more than 3mm should protrude.
How To Replace A Door Lock
How To Change A Euro Cylinder, Step By Step
- Open the door fully. Keep it wide open throughout so you can’t accidentally lock yourself out.
- Unscrew it and remove it. Pop it somewhere safe. You’ll need it again shortly.
- Turn the key slightly. Insert the key and turn it a little, around 15 degrees, so the cam lines up with the cylinder. This lets it slide out cleanly.
- Pull the old cylinder out. If it’s stubborn, wiggle it gently while turning the key. Don’t force it.
- Compare the new with the old. Check that the length and shape match before fitting.
- Slide in the new cylinder. With the key inside and turned to the same slight angle, push it in until the screw hole lines up.
- Refit the screw. Tighten firmly, but don’t overdo it.
- Test it. Only close the door once you’re happy everything runs smoothly.
Changing A Mortice Or Nightlatch
These take a little more patience. For a nightlatch, you’ll unscrew the case from the inside face of the door, remove the old cylinder and fit the new one. A mortice lock means removing the faceplate screws and sliding the lock body out of the door edge.
Common Mistakes To Avoid
We’ve seen the same slip-ups time and again:
- Buying the wrong size and not measuring first
- Fitting a cheap lock with no security rating
- Closing the door before testing the new key
- Over-tightening the screw, which can jam the mechanism
- Forgetting to ask for enough keys, or to cut spares for family
- Ignoring a warped or damaged door, which causes the lock to stick regardless of how new it is
When It’s Time To Call A Locksmith
DIY is great, but there are moments when it pays to call in a professional:
- You’re locked out and can’t open the door
- The lock is seized, broken or snapped in half
- Your door has a multipoint system that needs adjusting
- You need to meet strict insurance requirements
A reputable locksmith should be DBS checked, insured and clear about costs before they pick up a tool. Always ask for a price upfront and be wary of anyone quoting suspiciously low “from” prices over the phone.
Final Thoughts
Hope you have got your answer for how to replace a door lock. Changing a door lock isn’t glamorous, but it’s one of the most worthwhile jobs you can do around the house. Measure carefully, choose a lock with the right security rating, and take your time. And if it all gets a bit much, there’s no shame in handing it over to a professional like 24/7 London Locksmith.
Frequently Asked Questions
- How long does it take to change a door lock?
A euro cylinder usually takes 10 to 20 minutes, even for a beginner. Mortice locks and multipoint systems can take a bit longer.
- How much does it cost to change a lock in the UK?
A good anti-snap cylinder typically costs between £20 and £60 to buy. If you hire a locksmith, expect to pay more, depending on the lock type, time of day and your location.
- Can I change a lock myself if I rent?
Often you can, but check your tenancy agreement first. Many landlords need to give permission, and some insist on keeping a copy of the key.
- Do I need to change the whole lock or just the cylinder?
In most cases, the cylinder is enough. You’d replace the whole lock only if the body or mechanism is damaged, or it no longer meets your insurer’s standards.
- Will changing my lock affect my home insurance?
It can. Many policies require BS3621 locks on external timber doors, and a TS007-rated cylinder on uPVC doors. Check your policy documents, or call your insurer, before you buy.