How do I measure a euro cylinder before buying a replacement?

Measure from the centre of the fixing screw hole to the outside face of the door, then from the centre to the inside face. Write both figures down as a pair - for example, 35/45mm means 35mm on the outside and 45mm on the inside (80mm total). The most common UK sizes are 35/35, 40/40, and 45/45. Always measure before purchasing to avoid buying the wrong size.

Can I replace a uPVC door barrel lock myself?

Yes - replacing a euro cylinder on a uPVC door is a straightforward DIY job requiring only a screwdriver and tape measure. The whole process typically takes 15-30 minutes. The main risk is buying the wrong size, so measure the existing cylinder carefully first. If the fixing screw is seized, the door frame is misaligned, or you are unsure about the security rating needed, a locksmith is the safer option.

What is an anti-snap euro cylinder and do I need one?

An anti-snap cylinder has a sacrificial break line that snaps under attack while the main locking mechanism stays secure and the door stays locked. Cylinder snapping is the attack the TS007 standard was written to stop: it was developed by the Door & Hardware Federation and the Glass and Glazing Federation with Secured by Design, the police crime prevention initiative. Look for a TS007 3-star cylinder, or a 1-star cylinder paired with a 2-star handle, or a Sold Secure SS312 Diamond cylinder. Brands that make them include Brisant Ultion, Avocet ABS, Mul-T-Lock and Yale Platinum. Budget cylinders with no rating offer no snap protection and should not be used on an external door.

How much does it cost to have a locksmith replace a euro cylinder in London?

City Locksmith London charges from £69 labour (ex VAT) to replace a euro cylinder, with the part on top. A high-security anti-snap cylinder costs more than a basic one, so the total depends on the specification you choose and whether the job is routine or an emergency. There is no call-out fee and the price is fixed and agreed before work starts - see our locksmith price list for current rates.

How do I know if my uPVC door needs a new cylinder rather than just lubrication?

If the key turns stiffly but the lock still operates, silicone-based lubricant applied to the keyway will often restore smooth action. However, if the key is consistently hard to remove, the cam fails to engage the locking points, there is visible cracking or corrosion on the cylinder body, or the lock was subjected to a forced entry attempt, replacement is the correct course of action. A cylinder that intermittently works but then fails is also a sign that the internal mechanism is worn and should be replaced.

What size euro cylinder fits most uPVC doors in the UK?

The most common euro cylinder sizes for UK uPVC and composite doors are 35/35mm (70mm total), 40/40mm (80mm total), and 45/45mm (90mm total). However, sizes vary between manufacturers and door models, so always measure your existing cylinder rather than assuming. A cylinder that protrudes beyond the door handle is a security risk as it is easier to snap off - choose a size that sits flush or slightly recessed within the handle.

Will replacing the euro cylinder void my home insurance?

Replacing a euro cylinder will not void your home insurance provided the replacement meets or exceeds your policy's security requirements. Many insurers now specify a TS007 3-star or Sold Secure SS312 Diamond cylinder on uPVC and composite doors. Fitting a lower-grade replacement could affect a claim if a burglar gets in by snapping the lock. Check the policy wording, keep the receipt, and if in doubt fit a 3-star rated cylinder, which satisfies most standard UK home insurance requirements. The current versions are TS007-1:2024 and Sold Secure Diamond 2024.

How to Replace a uPVC Door Barrel Lock (Step by Step)

To replace a euro cylinder (barrel lock) on a uPVC door: measure the old cylinder from the centre of the fixing screw to each face of the door (for example 35/45mm), unscrew the single horizontal fixing screw on the door edge, turn the key about 10 to 15 degrees to align the cam, then pull the cylinder straight out. Fit the replacement by reversing those steps, and make it a TS007 3-star or Sold Secure SS312 Diamond anti-snap cylinder rather than a like-for-like budget one. The job takes 15 to 30 minutes and needs only a screwdriver and a tape measure. If you would rather not do it yourself, City Locksmith London fits cylinders across Greater London through its lock change service, from £69 labour (ex VAT), with no call-out fee and a fixed price agreed first.

When Does a Barrel Lock Need Replacing?

The euro cylinder - often called a barrel lock - is the part of a uPVC door a burglar attacks, because the multipoint mechanism behind it is only as strong as the cylinder that drives it. Knowing when to replace it prevents both a lockout and a break-in. For faults that are not the cylinder’s doing, see why a uPVC door will not lock, and for a fitting service see our uPVC locksmith page.

Replace your barrel lock if you notice any of the following:

Difficulty turning the key - Increased resistance or the key requiring significant force
Key getting stuck - The key jams or is hard to remove
Visible rust or corrosion - Particularly around the keyway or on the body of the cylinder
Frequent jamming - The lock intermittently fails to engage or disengage
Inconsistent operation - Works sometimes but not others
After a break-in or attempted break-in - Replace immediately, even if the lock appears undamaged
Outdated model - Older cylinders without anti-snap protection should be upgraded regardless of condition

Tools and Materials You Will Need

Tools:

Phillips and flat-head screwdrivers
Tape measure
Safety glasses and gloves

Replacing the cylinder alone needs nothing more than this. An Allen key is only required if you go on to work on the multipoint gearbox itself, which is a different job and not covered here.

Materials:

Replacement euro cylinder (correct size - measured before purchase)
Silicone-based lubricant
Cleaning cloth

Step 1: Measure the Old Cylinder Before Removal

Measuring first avoids a wasted trip to the hardware shop. With the door open and lock in the unlocked position:

Measure from the centre of the fixing screw to the outside face of the door
Measure from the centre of the fixing screw to the inside face of the door
Note the total length - e.g., 35/45mm means 35mm on the outside, 45mm on the inside (total 80mm)

This is your cylinder size. Buy a replacement of the same dimensions, or consult a locksmith if you are upgrading to a higher-security specification.

Step 2: Removing the Old Cylinder

Put on your safety glasses and gloves
Locate the fixing screw on the edge of the door (usually accessible when the door is open) - it runs horizontally through the door body into the cylinder
Unscrew it completely and set aside
Insert your original key and turn it slightly (approximately 10-15 degrees) to align the cam at the back of the cylinder with the slot in the lock body
Pull the cylinder firmly straight out from the door
If the door handle was obscuring access, remove it by unscrewing the handle screws on both faces
Clean the cylinder housing with a cloth before installing the new lock

Step 3: Choosing the Right Replacement Cylinder

When purchasing a replacement, prioritise security alongside size:

Anti-snap protection - look for a TS007 3-star cylinder, or a 1-star cylinder combined with a TS007 2-star handle. Cylinders are never rated 2-star; that rating belongs to the handle or escutcheon, and the stars add up to three. The current version of the specification is TS007-1:2024, published by the Door & Hardware Federation and the Glass and Glazing Federation, and it is the version Approved Document Q now points to
Sold Secure SS312 Diamond - the alternative route. Sold Secure tests the cylinder on its own, with no protective handle fitted, and Diamond is its top grade (currently Diamond 2024). It is treated as equivalent to a 3-star Kitemarked cylinder
Anti-pick and anti-drill features - to pass TS007 a cylinder must resist five attacks: picking, drilling, bumping, snapping and plug extraction
Reputable brands - Brisant Ultion, Avocet ABS, Mul-T-Lock and Yale Platinum all make rated anti-snap cylinders. Ultion is Brisant’s own brand, not a separate manufacturer
Correct fixing - ensure the cam profile matches your lock body (most UK uPVC doors use a standard euro cam)

Avoid the cheapest cylinders on the market - a budget lock fitted to a solid door is the weakest point in your security. Check the markings on the cylinder body itself rather than the words on the packaging: “anti-snap” is a marketing phrase, while the BSI Kitemark with three stars is a tested rating. If you would like a locksmith to supply and fit a high-security cylinder at a fixed price, see our locksmith price list for current rates.

Step 4: Installing the New Cylinder

Clean the cylinder housing thoroughly
Insert the new cylinder with the key in place, turning it slightly to align the cam
Slide the cylinder fully into the lock body until it seats correctly
Re-insert the fixing screw and tighten firmly - but do not over-tighten, which can distort the cylinder body and cause binding
Reattach the door handle if it was removed
Apply a small amount of silicone lubricant to the keyway

Step 5: Testing the New Lock

Do not close the door until you have tested the lock thoroughly with the door open:

Insert the key and turn in both directions - the action should be smooth
Check the cam engages and releases the locking points correctly
Test from both inside and outside using all keys provided
Engage the lock fully and attempt to open the door without the key - it should not move
Check that any additional keys (spare copies) also operate the lock correctly

Once you are satisfied, close the door and test from both sides with the door shut.

Common Mistakes to Avoid

Wrong measurements - the most common error; always measure before buying
Fitting an over-long cylinder - a cylinder that stands proud of the handle gives an attacker something to grip. Aim for flush or a couple of millimetres recessed on the outside face
Choosing a cylinder with no rating - a significant security risk on any uPVC or composite door
Over-tightening the fixing screw - Can cause the cylinder to bind or crack
Skipping the test phase - Always test before closing the door
Ignoring door condition - A warped door or misaligned frame affects how the lock operates

Additional Security Upgrades for uPVC Doors

Once your cylinder is replaced, consider these complementary measures. Our guide to high-security locks and when you need them covers the ratings in more detail, and how burglars break into houses in London explains what these upgrades are defending against.

Multi-point locking system - Engages the door at multiple points rather than just one
Door reinforcer - A metal plate that strengthens the area around the lock and letterbox
Sash jammers - Prevent the door being forced open even when locked
Anti-snap handle - A TS007 2-star armoured handle combined with a 1-star cylinder achieves the same 3-star protection level at lower cost
Door alarm sensor - Integrates with a home alarm system to trigger if the door is opened

Need Help Replacing a uPVC Door Cylinder?

City Locksmith London can replace your euro cylinder quickly and correctly, supplying and fitting high-security anti-snap cylinders across London. Our uPVC locksmith team specialises in these locks, and we also offer a complete lock change service if additional locks need upgrading. Lock change labour starts from £69 (ex VAT), there is no call-out fee, and our engineers are fully insured and DBS-checked.

Iulian H., lead locksmith at City Locksmith London, says: “We measure the cylinder against the door rather than the old part, because an over-long cylinder is the one thing that undoes an otherwise good lock.”

Contact a locksmith for a free quote, or see the full locksmith price list.

How to Replace a Barrel Lock in Your uPVC Door: Step-by-Step Guide