How to Change Upvc Door Lock

Changing a uPVC door lock is one of the most common and straightforward home security tasks you can carry out yourself. Whether you are re-securing after moving into a new house, replacing a broken cylinder, or upgrading to a higher-security anti-snap lock, the job typically requires nothing more than a screwdriver and 20–30 minutes.

uPVC doors use two distinct types of locking component: the euro cylinder (the barrel that your key turns) and the multipoint locking mechanism (the latches and bolts that engage into the frame). Most lock faults involve one or the other. This guide covers both.

Understanding Your uPVC Lock

Most uPVC front and back doors use a multipoint locking system, when you lift the handle and turn the key, multiple hooks, latches, or bolts engage simultaneously at different points up and down the door edge. The driving force is the handle-operated gearbox inside the lock body.

The euro cylinder is the replaceable barrel that your key operates. It sits in a hole in the door face, retained by a single screw, and connects to the gearbox via a cam at its back end.

Common problems and which component is at fault:

Changing the Euro Cylinder (Most Common Job)

Changing the cylinder is the right fix for most key-operation problems, and is also the standard action after moving to a new property.

What You Need

• Screwdriver to fit the cylinder retaining screw
• The old key (you need to operate the cylinder during removal)
• A replacement euro cylinder in the correct size

Measure the Cylinder First

Euro cylinders are measured as a total length and a split around the centre fixing hole. Yale, for example, states the internal size first, so its 40/50 euro cylinder is 40 mm on the inside and 50 mm on the outside, totalling 90 mm; check which way round your supplier lists them.¹

To measure: open the door, remove the existing cylinder (see below) and measure from the centre of its fixing-screw hole to each end.

Buying the wrong size is the most common mistake. A cylinder that is too short will not sit flush with the handles, while one that is too long sticks out where it can be gripped; Yale advises that a cylinder should protrude from the handle by no more than 3 mm.¹ If in doubt, take the old cylinder to the hardware shop.

Security Grade: Anti-Snap Cylinders

Standard euro cylinders can be snapped: a burglar grips the part that sticks out of the door and forces it until the cylinder breaks, usually at its weakest point by the fixing-screw hole, exposing the mechanism so the lock can be opened in seconds. Anti-snap cylinders have a sacrificial section designed to break off first, leaving the part that operates the lock in place.

Always specify an anti-snap cylinder, ideally one that also resists bumping, picking and drilling. Look for a cylinder with the TS 007 Kitemark and three stars, or a TS 007 1-star cylinder combined with a TS 007 2-star Kitemarked armoured handle.² The other nationally recognised standard is Sold Secure Diamond (SS312), and Secured by Design approval is another good sign.³ Most major lock brands sell 3-star cylinders, so check the Kitemark and stars on the exact cylinder rather than relying on the brand name.

West Yorkshire Police recommend a 3-star solution as the minimum when you upgrade a cylinder.³ For example, Toolstation listed a Yale Platinum TS 007 3-star 40/50 cylinder at £59.99 including VAT in September 2026.⁴

Step-by-Step: Cylinder Removal and Replacement

1. Open the door and leave it open throughout, you do not want to lock yourself out.
2. Locate the cylinder retaining screw on the edge of the door, in the faceplate of the lock, level with the cylinder.
3. Undo this screw and remove it completely: it passes through the body of the cylinder, so the cylinder cannot come out while it is in place.
4. Insert your key into the cylinder and turn it slightly until the cam lines up with the body of the cylinder. The cam must clear the gearbox for the cylinder to slide out.
5. With the key holding the cam retracted, slide the cylinder straight out towards you. It should come out smoothly. If it sticks, check the retaining screw is fully out and the cam is lined up.
6. Take the cylinder to the hardware shop if you have not pre-measured, staff can size a replacement from the old cylinder directly.
7. Insert the new cylinder by reversing the process: turn the key to retract the new cam, slide the cylinder into the hole, align the cam slot with the gearbox, release the key, and push home.
8. Tighten the retention screw, firmly, but do not overtighten or you will strip the thread.
9. Test with the door open: key should turn smoothly, and handle operation should engage and disengage the bolts correctly.

Replacing a Multipoint Locking Mechanism

If the cylinder is fine but the bolts or hooks are not engaging when the handle is lifted and key turned, the gearbox or mechanism needs replacing.

Identification

Remove the door handle (two screws on the rose or backplate) and the internal handle cover. The spindle hole and gearbox will be visible. Note:

• The backset, distance from the door edge to the centre of the spindle hole (commonly 35 mm or 45 mm, but other sizes exist)
• The case size, the height of the gearbox housing
• The handing, is the door left-handed or right-handed? (Stand facing the door from outside; if the hinges are on the left, it is left-handed)
• The cam follower position, where the euro cylinder cam engages the gearbox

Photograph the existing mechanism before removing it. Many mechanisms are brand-specific (Maco, Fuhr, GU, Winkhaus, Yale, Avocet). Match by photograph if the brand is not marked.

Replacing the Mechanism

1. Note the positions of all hooks, latches, and bolts on the door edge.
2. Remove all screws holding the mechanism to the door edge.
3. Slide the mechanism out of the door pocket, this can require patience on older doors where the mechanism has swollen or corroded slightly.
4. Fit the new mechanism in reverse: slide in, align all the bolt/hook positions with the keeps in the frame, screw in position.
5. Refit the handle, euro cylinder, and test thoroughly.

If you cannot identify the mechanism or it is a bespoke size, a locksmith is the practical option. Most locksmiths carry a range of common mechanisms and can identify and fit a replacement in under an hour.

When to Call a Locksmith

Call a locksmith rather than attempting DIY if:

• The door is locked shut and the cylinder or mechanism has failed, emergency entry is specialist work
• The mechanism brand cannot be identified and online research has not resolved it
• The door itself has dropped or the frame has moved, causing misalignment, this is a door hanging or frame repair, not a lock job
• The door is a composite rather than uPVC, the locking mechanism may differ

A locksmith typically charges £80–£200 for a standard daytime job (non-emergency) in 2026. Out-of-hours emergency call-outs often run to £150–£350. Always confirm the total price before they start work.

Insurance Implications

Check your home insurance policy’s schedule of locks. Many policies set lock conditions for external doors, commonly BS 3621 mortice deadlocks or an equivalent multipoint lock. If the lock does not meet your policy’s requirements, the insurer could use that as a reason not to pay out after a break-in.⁵ An anti-snap euro cylinder meeting TS 007 3-star is usually a safe choice, but confirm with your insurer.

If in doubt, call your insurer’s claims line and ask about lock requirements before purchasing a replacement.