How to Change a uPVC Door Lock: the Barrel, the Gearbox and What It Costs

A uPVC door has one lock and many locking points. The hooks, rollers and bolts down the edge of the door all run off a gearbox in the middle, and the gearbox is turned by the cylinder, the part you put the key in, which the trade calls the barrel or euro cylinder. So "change the lock" almost always means one of two jobs: swapping the cylinder, which is a screwdriver and five minutes, or replacing the gearbox or the whole strip, which is not. The Master Locksmiths Association puts it bluntly: every locking point is operated by the cylinder, which makes it "the weakest point". The guides that rank for this cover the swap and skip the two questions that decide whether it was worth doing: is it the cylinder at all, and is the new one any better than the old?

First, is it the cylinder?

Open the door and work the lock in mid-air. If the handle lifts, the key turns and the bolts throw with the door open, the lock is fine, and a lock that fails with the door shut is out of alignment. That is a hinges-and-keeps job, covered in how to adjust a uPVC door, and a new cylinder will not touch it. If the key turns with a click but the lock still does not work, Checkatrade says the barrel is working and the fault is the gearbox. If the handle will not push down at all, or flops with no resistance, the MLA points at the gearbox too, though a floppy handle can also be a broken spring cassette in the handle itself, which a new handle fixes. And if the handle will not lift with the door open, the MLA's advice is that it is often a lack of lubrication before it is a failed mechanism, so try that first. A lost key, or a cylinder you want to upgrade, is a cylinder job; the MLA notes that most locksmiths replace the lock after keys are lost. On a door fitted recently that has never locked cleanly, suspect the frame before the lock: how it should be packed and squared is in how to fit a uPVC door. A window that will not lock has its own list of causes, in what to do when a window will not close.

Measure the cylinder

A euro cylinder has two halves either side of a cam, the flat metal piece in the middle that works the lock, and its size is the length of each half. Measure from the centre of the cam, which lines up with the retaining screw hole, to each end: ERA's example is 37 mm inside and 40 mm outside. With the cylinder still in the door, measure from the centre of the screw hole to each end. A 35/35 is equal; a 35/45 is offset, with 35 mm on one side and 45 mm on the other, and many doors need an offset cylinder because the handles or the lock position differ inside and out (Lockstation). Common sizes run 30/30, 35/35, 35/45, 40/40, 40/50 and 45/45. Measure each side, not the overall length, which Ultion lists as a common mistake.

Two traps. First, the order: ERA and Yale both list the internal size first, but Lockstation warns that some suppliers measure differently, so write down which side is outside and check the diagram on the listing. Second, the old cylinder may never have been right. Four sources agree that a cylinder should sit flush with the handle or stand no more than 3 mmproud of it: ERA, Yale, the MLA and West Yorkshire Police, which says cylinders should not be left protruding from the door or handle. If yours sticks out further, a locksmith writing for The DIY Life says to measure from the screw hole to where it would sit flush, often visible as a weathered line on the cylinder, rather than to the end. And fit it the right way round: on a security cylinder the protection is on the outside half, marked EXT on ERA's.

A thumbturn cylinder has a key outside and a turn inside. Yale recommends one for a designated fire escape door, and the MLA says a thumbturn must be fitted in buildings with multiple occupancies, such as a house converted into flats. The MLA also lists thumbturn cylinders among the types at risk of snapping, so the same grade rule applies.

Swap it, step by step

You need the key; without it, Everest says, only a locksmith can change the barrel. With it, the job takes about five minutes and a screwdriver. Do it with the door open throughout.

1. Find the retaining screw. On the edge of the door, in line with the cylinder, is a larger screw than the rest, often a different colour. Undo it fully and keep it.
2. Free the cam.Put the key in and turn it slightly, until the cam sits inside the body of the cylinder. The makers put the angle at 5 to 20 degrees: Yale about 5, Screwfix 10 to 15, Ultion 10 to 20, ERA simply "slightly". The instruction to turn it to "10 or 2 o'clock" comes from locksmiths' how-tos; no maker's instructions we found use it. The one fetched version, a 2020 locksmith article, says about an eighth of a turn, which is 45 degrees and well past every maker's figure.
3. Pull it out by the key. If it resists, move the key a touch either way rather than forcing it (Ultion).
4. Fit the new one.Outside half facing out, key in, cam turned to sit centrally, and slide it in. ERA's rule is never to force a cylinder, which can damage it and void its warranty, and it warns that forcing a 3-star cylinder can snap it.
5. Refit the screw, firm but no more. ERA says never to use a power tool on it, and its screw may need cutting to length. Ultion warns that overtightening can distort the cylinder: if the door then locks but will not unlock, the screw is pressing on the body.
6. Test it open, then shut. Work the lock from both sides with the door open, then close it and check the bolts engage the keeps. Never use the key as a handle to pull the door, which is how keys bend and break.

On lubricant the makers disagree: ERA says a non-acidic oil such as 3-in-1, Screwfix says silicone or graphite and no oil-based products, Ultion a specialist lock lubricant. All three say not to use WD-40. Follow the instructions that come with your cylinder.

The commonest bad swap is a new anti-snap cylinder bought to the old one's size, standing well past the 3 mm limit from the handle. That is a worse lock than the one it replaced, whatever the packaging says. Measure to where the old one should have sat.

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Which cylinder to buy: stars and Diamonds

Two standards cover snap resistance. TS007, owned by the Door and Hardware Federation and developed with Secured by Design and the Glass and Glazing Federation, grades cylinders and handles in stars; Sold Secure's SS312 Diamond is the MLA's own. On TS007, a 1-star cylinder has basic approval and no snap testing, a 2-star rating is for handles and security escutcheons, and a 3-star cylinder has been tested for snap resistance. The DHF lists two ways to reach the protection it recommends: a Kitemarked 3-star cylinder, or a 1-star cylinder with a 2-star handle or lock surround. The MLA calls SS312 Diamond the harder test, with a heavier tool list and slightly less time, treats it as equivalent to 3-star for building regulations, and says more than 20 cylinders held the Diamond rating in 2026. A Kitemark means a third party did the testing, not the maker. The grade matters as much on a composite door as a uPVC one, and why the material does not decide security is in uPVC vs composite doors.

Source: Master Locksmiths Association (2026 guide); Door and Hardware Federation TS007 page; West Yorkshire Police euro-cylinder advice.

The police view is the same. West Yorkshire Police says a 3-star solution is the minimum to aim for when upgrading, and points out that a 3-star cylinder with a 2-star handle makes five. Greater Manchester Police, reporting a rise in lock snap burglaries in 2023, advised 2-star handles to TS007. How common snapping is rests on one force: West Yorkshire Police says around 10% of burglaries, and a freedom of information request to the same force, published by the MLA, put the share at 15.87% in 2011 and 8.32% in the first half of 2019. No national figure was found, so treat those as West Yorkshire's numbers, not Britain's. The MLA puts the time to snap an untested cylinder at 5 to 10 seconds, and one locksmith at 15; both are trade estimates. The MLA also notes that anti-bump is not anti-snap, and that only SS312 Diamond and 3-star cylinders are designed to snap and then lock up so the door stays shut.

Insurers are less specific than the packaging suggests. Allianz's guidance names a TS007 3-star cylinder for multipoint uPVC and composite doors and PAS 3621 for the lock itself; GoCompare says a typical minimum for uPVC doors is a key-operated multipoint lock with at least three locking points, and MoneySuperMarket says at least five for the main entrance. No insurer's policy wording was found making a 3-star cylinder a condition of cover. Read your own schedule. A 3-star cylinder costs from £64 as a part on the MLA's price list, and one retailer had a TS007 3-star cylinder at £44.99 on sale in September 2026, against from £27 for a budget one.

When it is the gearbox, not the barrel

The gearbox is, in the MLA's words, the central part of the multipoint lock. When it fails, the MLA says, the handle either will not push down at all or goes floppy, and on a door stuck shut with a loose handle it may take specialist opening techniques to get in. A partial lift that stops, with the key not turning fully, is misalignment, which the MLA says will wreck the gearbox if it is left; that is back to adjusting the door.

A replacement has to match. Three measurements can all be taken with the lock in the door: the backset, from the edge of the faceplate to the centre of the cylinder, almost always 35 mm on UK uPVC doors and occasionally 45 mm; the PZ, from the centre of the spindle to the centre of the cylinder, very often 92 mm but 62 mm and others exist; and the faceplate width, commonly 16, 20 or 22 mm. Note too whether the spindle is single or split and how many followers the gearbox has. The retailers' advice is to replace like for like, same make and size, and never to assume a size.

Whether to do it yourself is where the sources split. Checkatrade calls a broken gearbox "a very complex job" and recommends a locksmith; the MLA says fitting your own lock is not advised; Screwfix says multipoint gearboxes can need specialist tools. Against them, the makers publish DIY instructions (Yale and ERA both do), and a lock retailer says the right-sized gearbox is a screwdriver and five minutes, though that retailer sells the part. A fair line between them: a gearbox of the same make and size, swapped on a door that opens, is within reach of a careful DIYer with the maker's instructions. A full strip that has to be cut to length, where ERA warns not to cut the drive bar until the face bar is done, or a door stuck shut, is a locksmith's job. The MLA puts a gearbox swap at from about 30 minutes, longer on a French door.

What it costs in 2026

Source: Master Locksmiths Association price list and FAQ pages (2025 to 2026); Checkatrade uPVC door lock replacement cost (January 2025); MyBuilder and Keytek (2026); retailers on 19 September 2026. Research in lib/research/upvc-door-lock-2026.md.

The cylinder figures agree to within a few pounds. The MLA's price list, which it says averages its approved locksmiths' prices across the UK, has a standard cylinder changed from £105 and an anti-snap one from £137, each from about 20 minutes. Checkatrade's January 2025 guide sits a little lower, £75 to £125 and £100 to £150, and Keytek, a national locksmith, a little higher, from £125 and £150.

The gearbox is where a single number misleads, because repair and replacement are different jobs at different prices. The MLA's own price list has "Repair uPVC Gearbox" from £85, and adds that it may be cheaper to replace than repair; MyBuilder has repair at £60 to £80. A fitted replacement is dearer: the MLA's page on a floppy handle puts it at £145 to £280, and its page on a handle that will not lift at £175 to £335, both including labour. Checkatrade's £90 average for a gearbox replacement, from January 2025, sits with the repair figures rather than the MLA's replacement ones. Ask which you are being quoted for. A full new multipoint strip is £120 to £300 on Checkatrade's figures; the MLA puts the parts alone at £76 to £263 or more, before labour, so dearer makes can pass £300.

On call-out fees the sources disagree. The MLA says most emergency locksmiths do not charge one; MyBuilder lists £50 to £150 out of hours and Keytek an evening and weekend call-out at £100 to £130. The MLA also points out that there is no governing body for locksmiths, so they can charge what they like. Ask for the total, and what the call-out covers, before anyone sets off.

Locked out, a broken key or a snapped cylinder

An MLA-approved locksmith will usually try non-destructive entry first, and the MLA is clear that drilling should be a last resort; a rogue locksmith drills first because a damaged lock is a bigger invoice, and a bill with several item charges after drilling is its warning sign. Opening a locked door costs from £90 on the MLA's list. For a key snapped in the lock, the MLA says trying to get it out yourself is probably the worst thing you can do; a straightforward extraction of half an hour or less is around £85. A cylinder that has been snapped should go back as 3-star or Diamond: no source puts that as a rule in so many words, but it follows from the police advice on upgrading and from the MLA's point that every locking point runs off the cylinder.

If the lock is the least of the door's problems

A worn cylinder or a tired gearbox is a repair, and the figures above are the whole cost. Where the door has also dropped, bowed or started letting the weather in, the repairs add up against a new door, which the door cost calculator prices by type. If you want a replacement priced on your own opening, tell us what you need and Leads 2 Trade will arrange quotes from installers covering your postcode.

Price-checkedLast reviewed 19 September 2026

Reviewed byDouble Glazing Cost Calculator TeamCross-checked against Checkatrade, the FMB & GreenMatch