Guide
How to Change the Lock on a uPVC Door: Barrel, Handle or Mechanism
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Working Out Which of the Three Jobs You Are Doing
Choose between three jobs before starting: replacing the barrel, renewing the handle set, or changing the multipoint mechanism housed in the door edge. Begin with what happens when you use the key. Will it turn without securing the door, refuse to turn, or work normally when all you need is a different set of keys?
Changing the Barrel: The Five Minute Job
A euro cylinder, also called the barrel, is usually the simplest replacement. If the existing lock works and you want new keys, changing this part may be enough. Its retaining screw sits in the faceplate. Check the required measurements and compatibility with the hardware staying on the door before buying; appearance and brand cannot establish fit.
For TS 007 protection, choose either a three-star cylinder Kitemarked to TS 007 or a one-star cylinder Kitemarked to TS 007 paired with two-star protective hardware Kitemarked to TS 007. These ratings apply specifically to cylinders and protective hardware; they do not certify an entire door or its multipoint mechanism. The words anti-snap alone establish no recognised test result.
The Two Bigger Jobs: The Handle and the Mechanism
A loose or broken handle calls for a matching handle set and further measurements. Locking points that remain still may indicate gearbox or mechanism trouble. A qualified locksmith can identify the exact edge-mounted system and replace it. Use the sizing, testing and fitting guidance only while the door opens safely and every part moves without force.
Before You Buy Anything, Measure the Cylinder
Two numbers decide whether a new euro cylinder fits, and both are measured from the centre of the fixing-screw hole, not taken from the barrel you happen to remove. A size such as 35/35 or 40/50 gives the length either side of the cam. With the cam's 10mm added, a 35/35 cylinder is 80mm long, and a 40/50 is offset, longer on one side.
How Copying the Old Barrel Can Make the Door Worse
The barrel in the door may already be too long. If it projects past the handle plate by more than about 3mm, an identical replacement keeps that overhang, which is what makes a cylinder easier to attack. Trade guidance treats 2mm to 3mm beyond each plate as acceptable. A barrel that is too short sits sunk inside the handle, the key catches and the screw may not meet its thread.
Where to Measure From, and the Five Millimetre Rule
Open the door and locate the cylinder retaining screw on the faceplate, normally level with the cylinder. Measure from its centre to the outside face of the external handle or security escutcheon, then from that same centre to the inside face of the internal handle. Note each figure separately and mark the outside. Cylinders are made in 5mm steps, so 43mm generally rounds to 45 and 42mm to 40, but confirm the sizes available and the finished position before you round.
- Reference point: the screw-hole centre.
- Size steps: 5mm.
- Protrusion: about 3mm at most.
Confirm key or thumbturn inside too, and see why an overhanging cylinder is the weak point.
Undo the Fixing Screw Set in the Edge of the Door
Everything in this step happens on the edge of the door, so open it fully. Down that edge runs a metal faceplate, and close to keyhole height is the cylinder retaining screw. It is longer than its neighbours because it travels through the faceplate into the threaded centre of the cylinder.
Confirm that is the screw you are looking at, because the others secure the locking strip and should stay put. Undo the retaining screw until it comes out, then put it somewhere safe. If it is damaged or incompatible with the replacement, plan to use the correct screw supplied or specified with the new cylinder.
About the handle: it can stay on for most uPVC doors. The exception is a handle plate or escutcheon that covers the screw or the face of the cylinder; loosen that plate's own fixings and carry on, without levering anything.
Check your hand: one screw. Check the door: a cylinder that has not moved yet.
Collect the Tools Needed for This Job
Gather three things for a barrel change: a screwdriver, something to measure with, and the new part.
- The screwdriver needs a long, thin shaft, as the fixing screw is recessed in the faceplate on the door edge.
- A steel rule or tape takes the measurements.
- The new cylinder comes with its keys and must match the sizes you recorded.
Use the existing working key as well, because the old cylinder needs it to come free. Two items depend on your door. If the handle has to come off, add an allen key or a small screwdriver, and if the edge of the door is dark, add a torch. New handles bring their own requirements: a compatible set, the right spindle and fixing screws, and a suitable screwdriver.
A drill is never part of this job. Put the long fixing screw straight into a pot or pocket, since it is easily dropped and carpet swallows it.
Make Sure the New Cylinder Is Fitted the Right Way Round
The longer end goes inside the house. Confirm that before the barrel enters the door, because an offset cylinder fitted backwards leaves the door weaker than it was before you began. Put the thumbturn, if there is one, on the inside too.
Fitting
Align the cam by turning the new key slightly, then slide the cylinder in from outside, gently. Tiny key movements let it seat fully; it should never need pushing. Should it catch, withdraw it and check its dimensions, which way round it sits and the position of the cam. A fingertip on the face helps you line up the threaded hole with the screw opening in the faceplate. Fit the correct screw and tighten until the barrel holds, without overdoing it.
Two Checks
- Does it stay still in the door, sit properly within the handle plates and stand no more than about 3mm proud outside?
- Does the key go in, turn and come out without binding from both sides? If the screw made it stiff, loosen and recheck.
Directional cylinders are marked so you can tell which face is external. Force, filing and packing are never the answer: a cylinder that does not fit is the wrong cylinder, which may also raise whether the door needed a repair rather than a new barrel.
Line Up the Cam and Draw the Cylinder Out
Think of the cam as a latch on the barrel itself: until it lines up with the cylinder body, the barrel stays where it is. Slide in the key that works the lock and turn it gently, by about 45 degrees. Some locks want left, some want right, so test one way and then the other rather than pushing. Once you feel the cam settle in line, hold the key there, take hold of the cylinder where possible and ease it sideways out of the door. If it hesitates, shift the key by a very small amount.
What-if: - Will not move with the cam in line? The fixing screw is probably still in, because nothing else retains it. Check it is out fully. - Still stuck? See whether a handle plate is gripping it or the barrel is damaged or distorted, and stop rather than force it.
Avoid pulling hard on the key or levering with it. The old cylinder stays in a drawer until the new one is tested.
Test the Door Before You Walk Away
Test it open before you test it shut, and do that every time you fit a cylinder. Here is the sequence.
- With the door open, insert and remove the key from both sides, or turn the thumbturn, then lift the handle and lock as normal. Hooks, rollers and bolts should extend and retract along the edge; if there is a trigger, use the manufacturer's test method.
- Retract every locking point, bring the door gently to the frame without locking, and confirm it closes naturally with the latch meeting the keep.
- Shut it fully and operate the handle and key, with no force, from inside and from outside.
Why that order? Because a lock that works with the door open but not with it closed is reporting on the door, its hinges or its keeps, not on the barrel you just fitted. A lock that is stiff while the door is still open points back to the cylinder: recheck its size, fitting and compatibility before the door is used. A new part should never need excess pressure, and assuming it will wear in only invites damage. The final check is the keys, every one of them, tried from both sides, spares included.
If Any of This Applies, Stop and Call Someone
This guide only holds while you have a working key and a door that opens. Outside that boundary are four stopping points: the key is missing, the key has snapped, the door is locked shut, or the cylinder turns and nothing happens. If the door cannot be kept open and secure, the component cannot be identified or a part needs force, carrying on risks damage to the door, the frame or the whole lock.
If There Is No Key or the Key Has Snapped
There are ways to remove a euro cylinder without its key. We will not describe them, here or anywhere on this site, because a technique that opens your door opens any door. In practice the cylinder is destroyed during removal and a new one goes in, so the end result is the part you meant to buy. A broken key is different: the cylinder itself may be perfectly sound once the broken piece is out.
If the Key Turns and Nothing Happens, or the Door Will Not Open
Neither is a barrel fault. A locked-shut door with a normally turning key suggests the mechanism or alignment. A handle or key that moves while the hooks stay engaged suggests the gearbox. Do not force either.
Damaged doors after a break-in, fire doors and communal or managed flat entrances also need a professional. Note whether the door is open, closed or locked shut, whether the property is secure, and any markings, then contact.
Get It Changed Instead
Whether you have finished the job or decided not to start it, B.T Locksmiths Hastings can change uPVC cylinders and mechanisms across Hastings when the size is uncertain, the key has gone or the door is resisting. Plenty of people fit their own barrel, and the guide above holds; this is the alternative. Calls are free of any call-out charge, whatever the hour, and emergency calls are answered around the clock all year. The price is given on the call, based on your description.
Useful to have: the door material, a note on whether the key turns, and a photograph of the edge and the handle.
Get a Price for a uPVC Lock Change: 01424 571056
Or book a uPVC lock change with B.T Locksmiths Hastings, and see our lock replacement service for more.
uPVC Door Lock Questions
Can I change a uPVC door lock without the original key?
Not generally through the standard cylinder replacement process. That method normally depends on a working key to bring the cam into alignment, so removal without a key may need a qualified locksmith. Removal of the cylinder and handle set, along with the multipoint strip, normally takes place with the door open. Do not apply the standard procedure to a door locked closed, or force or take apart the lock with its locking points engaged in the frame.
Can I change a uPVC door lock if the door will not open?
Not through the standard replacement steps if the door is locked shut. Ordinary access for removing the handles, cylinder and multipoint strip is with the door open. The usual DIY cylinder method is also generally unsuitable without a usable key, which normally aligns the cam. Professional removal may be required where no key is available. Keep force and dismantling out of the process while the locking points are still engaged with the frame.
How do I know whether the cylinder or gearbox has failed?
A key that cannot enter or turn may point towards the cylinder or the key itself. That is an inspection starting point, not confirmation of a failure. If turning produces no movement at the locking points, examine the multipoint mechanism, gearbox, cylinder connection and spindle.
Can I replace the barrel without changing the multipoint mechanism?
Yes, a euro cylinder is generally replaceable as an individual part. For new keys or a security improvement, changing that barrel may be all that is needed. This depends on correct operation throughout the handles, the gearbox and the door's locking points.
Do I need to remove the handles to change a euro cylinder?
Removing the handle set is not normally necessary. Most euro cylinders come out once their retaining screw has been removed and the key has aligned the cam. Obstruction is the exception: the handle plates or the surrounding protective fittings may require loosening if they prevent the cylinder from coming out.
Are all uPVC door handles the same size?
A single handle size will not suit every uPVC door. Operation, spindle layout, backplate size, screw fixing locations and PZ centres can all differ. Measuring the existing set before ordering is therefore necessary. Include door thickness in those checks, as it can affect the spindle and screw lengths needed.
Why does my uPVC door lock work when open but not closed?
This usually suggests resistance where the door's locking points meet the frame. Possible causes include a dropped door, worn hinges or a mismatch between the keeps and the latch, hooks or bolts. Those alignment issues may explain why the mechanism works with the door standing open.
Can I replace only the gearbox in a uPVC door lock?
The gearbox alone may be changed when a matching replacement is available. Match the spindle arrangement and backset, together with PZ centres, fixings and the connections between the gearbox and locking strip. If that strip is damaged or worn, or other locking points are, replace the complete mechanism.
Can I replace a multipoint lock with a different brand?
Changing brands may be possible with a replacement mechanism designed for compatibility. Compare the gearbox, operation, faceplate, locking point positions and measurements: each must match the door. Using different locking points may additionally require the keeps in the frame to be changed.
What happens if I fit the wrong-size euro cylinder?
Excess length may leave more cylinder showing beyond the external protective fittings. Too little length may put it so far back that using the key becomes difficult. Before placing an order, take separate measurements for the internal side and the external side of the cylinder.
Do I need to replace the complete lock after losing my keys?
A complete lock change is not normally needed. Replacing the euro cylinder should prevent the lost keys opening the door, provided that cylinder is what they operate and the rest of the system functions correctly. Any other keyed locks should also be checked for a possible need for attention.
Why is the new uPVC door handle still drooping?
The handle set may not be the only part involved. Its springs, the spindle, the way the fixings align or the internal gearbox could explain the droop. Recheck sizing and fitting with the door open, without assuming a handle replacement will correct a gearbox fault.