How to Replace a Door Lock Cylinder (Euro Cylinder)
Measure, buy and fit a replacement euro cylinder on a UK uPVC or composite door, including the snake-proof standard, correct length and a tidy fitting.
Changing a euro cylinder is one of the most useful home security jobs and one of the easiest. It is the barrel in the middle of the door lock into which you put the key. Fitting a better one takes ten minutes with a screwdriver, provided you buy the right length and keep the door open while you work. Here is how.
When to replace the cylinder
- You have moved house and do not know who has keys
- A key has been lost or stolen
- The lock is stiff, worn or difficult to turn
- Your cylinder is old and does not meet current security standards
- You are upgrading to a higher-security product
Replacing a cylinder is different from replacing a whole multipoint lock, which is more involved and often needs a locksmith or door specialist.
What you will need
- A new euro cylinder of the correct length
- A Phillips or flat screwdriver, depending on the fixing
- A tape measure
- Your existing key, which you will use to turn the cylinder and align the cam
Step 1: Identify the type
Most uPVC and many composite doors use a euro profile cylinder, which is shaped like a figure of eight in cross-section and is held in by a single retaining screw in the edge of the door. If your door has a different type of lock, such as a mortice sash lock, this guide does not apply.
Step 2: Measure
Cylinder length is measured in two parts, from the centre screw hole to each end, one for the outside and one for the inside, such as 40/45. To measure:
- Undo the retaining screw in the door edge, usually with the door open. Note the position, as it is held at the centre.
- Turn the key slightly, usually about 90 degrees, so the cam aligns with the body, then pull the cylinder out.
- Measure from the centre screw hole to the end of each side.
- Fit the same sizes. A cylinder that sticks out too far on the outside makes it easier to attack, so it should be nearly flush with the handle plate, ideally no more than 3 mm proud.
Take the old cylinder to a shop to compare sizes, or buy a measuring tool that shows the required length.
Step 3: Choose the security level
Look for cylinders that meet recognised security standards for resistance to snapping, bumping, drilling and picking. Many are marked with a kitemark or a star rating. Insurance policies sometimes specify a standard, so check your policy wording. Better cylinders cost more, but compared with the cost of a break-in, the difference is small.
Step 4: Fit it
- Open the door and keep it open so you cannot lock yourself out.
- Remove the retaining screw and take out the old cylinder.
- Put the new cylinder in, with the key turned to the same position so the cam lines up.
- Align the screw hole with the hole in the cylinder.
- Insert and tighten the retaining screw. Do not overtighten.
- Test the lock several times with the door open, and then closed with the door still ajar if possible.
- Check that the bolts extend and retract smoothly.
Check that the lock engages properly when the door is shut. If it is stiff, the door might be misaligned, so see how to fix a sticking door.
Common mistakes
- Buying a cylinder that is too long or too short
- Leaving the door shut during the swap
- Over-tightening the screw
- Using a cylinder that does not meet the required security level
- Not testing with the door open before closing
Tenants and landlords
If you rent, check your agreement before changing a lock, and keep the old one to reinstate when you leave. Landlords should give tenants a record of keys. See handyman work in rented homes and hiring a handyman for a rental property.
When to call a locksmith or handyman
If the lock is stuck, you are locked out, or the door has a multipoint lock mechanism that is faulty, a locksmith is the right person. For a simple cylinder swap, many handymen can do it in minutes as part of a longer visit. Pricing is typically modest; see handyman minimum call-out charges for how short jobs are charged.
On Compito, you can send a request with your postcode, ask the provider about security ratings, compare offers from ID-verified local providers and pay online when you accept.
Frequently asked questions
Do I need to change the locks when I move in?
It is a sensible precaution because you cannot know who has copies of the keys.
What does snap-proof mean?
It means the cylinder is designed to resist a common attack where the lock is snapped. A recognised standard or kitemark helps you check.
Can I fit a cylinder on a wooden front door?
Euro cylinders are used in some wooden doors, but older wooden doors often have a mortice lock, which is different. Check what you have before buying.