If you're looking to replace the cylinder lock on a uPVC door. You've come to the right place. uPVC cylinder locks are the most common lock type fitted to double-glazed doors in the UK. They're also one of the most frequently misunderstood when it comes to sizing, security ratings, and compatibility. This guide explains exactly what you need to know: How uPVC cylinder locks work; How to measure yours correctly; What security standard to insist on, and how to carry out a straightforward DIY swap.
What Is a uPVC Cylinder Lock?
A uPVC cylinder lock. More accurately called a euro profile cylinder; is the removable barrel lock fitted into the faceplate of a uPVC door. It's the component that your key directly interacts with. The cylinder operates the multipoint locking system. When you insert and turn the key, the cylinder's internal cam rotates and drives the deadbolts, hookbolts, and rollers of the multipoint lock into (or out of) the frame.
Crucially, the cylinder and the multipoint lock body are separate components. When a uPVC door lock fails, it's often the cylinder that needs replacing. Not the entire multipoint lock mechanism. This makes cylinder replacement a cost-effective and relatively simple repair in most cases.
Why uPVC Doors Are Vulnerable and Why the Cylinder Matters
uPVC doors fitted with poor-quality or incorrectly sized cylinders are among the most common targets for forced entry in the UK. The primary attack method is lock snapping: a burglar applies rotational force to the protruding end of the cylinder, snapping it at its weakest point and gaining direct access to the lock cam. Bypassing the door entirely in seconds.
The vulnerability has two causes. First, many older uPVC doors were fitted with standard cylinders that offer no snap resistance. Second, cylinders that are oversized for the door profile protrude beyond the faceplate, creating a lever point that makes snapping trivially easy. Both issues are solved by upgrading to a correctly sized, anti-snap-rated cylinder.
How to Measure a uPVC Cylinder Lock
Getting the measurement right is the most important step. Fit a cylinder that's too long and it protrudes past the faceplate, creating a snap risk. Fit one that's too short and the cam won't reach the lock body properly.
Euro cylinders are measured in the format: External (mm) / Screw Centre (mm) / Internal (mm). The screw centre is always 10mm, so the measurement is typically written as external x internal - for example, 35/10/35 or 40/10/40.
Step-by-Step Measuring Guide
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Open the door. Locate the retaining screw set into the edge of the door, roughly in line with the cylinder. It's typically an 8mm cross-head screw. Undo it two or three turns.
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Insert the door key and turn it slightly - just enough to move the cam and allow the cylinder to slide free.
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Remove the cylinder from the door. You'll now have it in your hand for accurate measurement.
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Measure from the outside face to the centre of the screw hole. This is your external measurement.
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Measure from the centre of the screw hole to the inside face. This is your internal measurement.
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Your replacement cylinder should match these dimensions exactly.
Common uPVC Cylinder Sizes
Most uPVC doors take one of four standard sizes. The format is always external / screw centre / internal, with the screw centre fixed at 10mm:
- 35/10/35 is the most common size by far and should be your starting assumption on any standard uPVC door - but always verify by measuring before ordering.
- 30/10/30 appears on slimmer-profile uPVC doors and some older installations where the frame is shallower than current standard.
- 40/10/40 is used on thicker uPVC profiles and some composite-style uPVC systems where the door panel is deeper.
- 30/10/40 or 35/10/45 are offset sizes, used where the cylinder sits asymmetrically within the door - closer to the outside face than the inside, or vice versa.
Trade Tip: Measure the existing cylinder before ordering - never assume 35/10/35 even on a "standard" uPVC door. Profile thicknesses vary by manufacturer and era. Getting the wrong size is the single most common avoidable callback on cylinder replacement jobs.
Which Security Rating Should a uPVC Cylinder Lock Have?
For any external uPVC door, the minimum security specification you should fit or recommend is a TS007 1-Star Anti-Snap Cylinder. TS007:2014 is the British Standard for euro cylinder locks, and it requires cylinders to pass independent testing for snap, drill, bump, and pick resistance.
1 Star vs 3 Star: Which Do You Need?
A TS007 3-star cylinder achieves full TS007:2014 compliance as a single product. It's the highest standalone rating available. Products such as the Yale Platinum 3* and the Avocet ABS Master 3* fall into this category. They both carry Secured by Design (SBD) Police approval.
A TS007 1-Star cylinder provides excellent protection but achieves overall TS007 compliance only when combined with a 1-star rated door handle and 1-Star letterplate (the "3+1+1 rule"). For most residential uPVC door replacements, a 1-star cylinder in combination with appropriate hardware is perfectly sufficient and cost-effective.
Note: For a uPVC door to be TS007:2014 compliant, it needs either: (a) a single 3-star rated cylinder on its own, or (b) a 1-star cylinder combined with a 1-star door handle and a 1-star letterplate. This "3+1+1 rule" is the standard required by Secured by Design, PAS 24, and many insurance policies.
Anti-Snap Cylinders: Non-Negotiable for uPVC Doors
The construction of most uPVC doors. A thin, relatively flexible frame with the cylinder protruding through the external faceplate. This makes them particularly susceptible to snapping attacks without a snap-resistant cylinder. This is not a niche concern: lock snapping accounts for a significant proportion of domestic burglaries in the UK, particularly in terrace and semi-detached properties with double-glazed uPVC doors.
All TS007-rated cylinders include a snap-safe feature: a designated break point positioned such that if the outer section is fractured, the inner lock mechanism remains intact and the door stays secure. Some higher-spec cylinders; including the Avocet ABS Master range add active snap protection. A secondary internal locking bar that deploys automatically if snapping is attempted.
If you're replacing a cylinder on a uPVC door and the current cylinder has no TS007 rating marked on it, treat it as non-compliant and upgrade as a matter of priority.
How to Replace a uPVC Cylinder Lock
Replacing a uPVC door cylinder is a job most confident DIYers can complete in under 15 minutes. You'll need a cross-head screwdriver (usually PH2 or PH3) and the correctly sized replacement cylinder.
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Open the door fully so you have access to both faces and the door edge.
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On the door edge (the part that faces the frame when closed), locate the fixing screw in line with the cylinder. Undo it 2-3 turns - there's no need to remove it completely.
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Insert the key into the outside of the cylinder and turn slightly. This moves the cam (the internal tongue) so it no longer catches on the lock body.
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While keeping the key slightly turned, slide the cylinder straight out of the door. It should move freely.
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Take the removed cylinder to match the dimensions before purchasing your replacement if you haven't already done so.
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Fit the new cylinder: insert it into the door, aligning the cam with the lock body slot. Use the key to position the cam if needed. Slide
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Home, tighten the fixing screw securely.
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Test the cylinder operates smoothly with the door open. Check that the multipoint lock extends and retracts fully. Close and lock the door to confirm.
Trade Tip: After fitting a new cylinder, check that it sits flush with - or fractionally recessed into - the external faceplate. No part of the cylinder should protrude more than 3mm beyond the plate. If it does, you need a shorter external measurement. A protruding cylinder on a uPVC door undermines even the best security rating.
When to Replace a uPVC Cylinder Lock
Beyond the obvious scenarios - lost keys, moving into a new property, or a break-in attempt - there are several indicators that a uPVC cylinder lock should be replaced:
- The key feels stiff or requires jiggling to operate smoothly. Internal wear reduces the reliability of the pin mechanism over time.
- The cylinder has no TS007 rating. Any cylinder without a star rating should be considered a security liability on an external door.
- The cylinder protrudes noticeably beyond the door faceplate. A sign it was incorrectly sized on original fit.
- You've had tenants change or you're letting a property. Rekeying via cylinder replacement is faster and more secure than collecting and verifying old keys.
FixTrade.co.uk supplies a full range of uPVC door cylinder locks. Including: TS007 1-star and 3-star anti-snap options, thumb turn cylinders, and standard euro cylinders across all common sizes. Trade accounts welcome. Browse the full cylinder lock range.