Locksmithing
How to replace a euro cylinder lock
Swapping a euro cylinder is one of the quickest security upgrades on a uPVC or composite door. The whole job hinges on measuring it properly.
What you'll need
- •Tape measure or steel rule
- •Long thin screwdriver (usually PZ2)
- •New cylinder and keys
Step by step
1Measure from the centre out
Measure from the centre of the cylinder's fixing screw hole to the outside face, then to the inside face. A cylinder written as 35/45 means 35mm outside, 45mm inside — the two halves are rarely equal.
2Remove the fixing screw
Open the door and take out the single long screw in the edge of the door, below the cam, through the faceplate.
3Turn the key to free the cam
Put the key in, turn it roughly 10–15 degrees so the cam sits within the cylinder body, then pull the cylinder straight out. If it won't move, the cam isn't aligned.
4Fit the new cylinder
Slide the new cylinder in the same way with the key turned, line up the screw hole and refit the fixing screw. Don't overtighten — it can bind the mechanism.
5Test before you close the door
Lock and unlock with every key, from both sides, with the door open first. Then test it closed.
Common mistakes
- •Buying a cylinder that projects past the handle — an exposed cylinder can be snapped. Aim for flush or under 3mm proud.
- •Measuring the old cylinder end to end and halving it; the halves are usually different lengths.
- •Fitting a basic cylinder to a door insurers expect to carry an anti-snap, 3-star or TS007-rated one.
When to get a second opinion
If the key turns but the door won't lock, the problem is usually the gearbox or alignment, not the cylinder.
Ask an experienced tradesperson