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.
Measure the Cylinder Before You Buy Anything
The most useful rule here is to measure from the centre of the fixing-screw hole to each end, and not to trust the size of the barrel currently fitted. A cylinder labelled 35/35 has 35mm on each side of the cam, and the cam adds 10mm in the middle, so the whole barrel is 80mm. An offset size such as 40/50 is 40mm one way and 50mm the other, so direction matters.
How Copying the Old Barrel Can Make the Door Worse
Plenty of doors already carry a barrel that is too long. It stands proud of the handle plate, and ordering a matching one keeps that overhang. Trade guidance sets a ceiling of about 3mm of protrusion, accepting 2mm to 3mm beyond each plate. The opposite fault, a barrel that is too short, leaves the face recessed, the key awkward to use and the screw hole possibly out of line.
Where to Measure From, and the Five Millimetre Rule
With the door open, find the retaining screw on the faceplate, which is normally level with the cylinder. Measure from the middle of that screw to the outer face of the external handle or escutcheon, then to the inner face of the internal one. Keep them as two separate numbers and mark the outside. Since sizes run in 5mm steps, 43mm usually rounds to 45 and 42mm to 40, but check the stocked sizes and the finished position first.
Quick check before buying: both readings, which end faces out, key or thumbturn inside, and how the face lines up with the handles. Then read why an overhanging cylinder is the weak point.
Undoing the Fixing Screw in the Edge of the Door
Swing the door open, then follow the metal faceplate on its edge down to the level of the keyhole. The retaining screw sits there, in line with the barrel, and it threads into a hole in the middle of the cylinder. You can usually tell it apart because it is longer than the screws holding the locking strip.
Removing It
Check you have the right screw. Unscrew it fully with a screwdriver that fits, take it out and set it aside where it will not get lost. Every other screw on the faceplate belongs to the multipoint strip, so leave those alone. If the screw is damaged or does not suit the replacement cylinder, use the correct screw that comes with or is specified for the new one.
If the Handle Is in the Way
Most of the time it is not. Where a handle plate or escutcheon covers the screw or the cylinder face, loosen that plate's fixings; nothing should need force.
You now hold one screw, and the barrel is still in the door.
Collect the Tools This Job Needs
Three items cover a straightforward barrel swap, and a ruler counts as one of them.
- Screwdriver: long and thin, because the fixing screw sits well inside the faceplate on the door edge.
- Steel rule or tape: for the two readings either side of the cam.
- New cylinder and keys: bought to the size you measured.
The existing lock's working key is needed too, to line up the old cam. If the handle is in the way, add an allen key or small screwdriver; if the door edge is badly lit, add a torch. Neither is needed on most doors. Where the handles are also being replaced, bring a compatible set, its correct spindle and fixing screws, and a suitable screwdriver.
You will not need a drill at any point. Give the long fixing screw a home before you remove it, because once it lands in carpet it can take a while to find.
Fitting the New Cylinder the Right Way Round
Confirm the longer side of the new barrel is the one going inside the house before you fit it. Reversing an offset cylinder is the mistake that leaves a door less secure than it was, and the same check puts a thumbturn on the inner side.
Sliding It In
Insert the new key and turn it slightly to bring the cam in line. Feed the cylinder into the opening from outside, gently, adjusting the key by small amounts until it seats fully. It should slide, not be shoved. Remove it if it snags, then recheck its size, orientation and cam position. Hold the face with a finger while lining the threaded hole up with the faceplate opening, then fit the correct retaining screw. Tighten it until the cylinder is secure, and stop there.
Checking the Result
- The barrel does not shift in the door, sits properly inside the handle plates and projects no more than about 3mm outside.
- The key enters and turns without binding from each side; if the screw has made it stiff, loosen it and reposition.
Many cylinders are marked to show the outside face. One that needs force, filing or packing is the wrong part, and that raises whether the door needed a repair rather than a new barrel.
Line Up the Cam and Draw Out the Cylinder
Turning the cam is the step that most guides skip, and it is why so many barrels seem welded in place. The cam is the small tab at the centre of the cylinder, and it must line up with the body before anything slides. Put in the working key and turn it slightly, around 45 degrees, in whichever direction your lock needs; try one way, then the other, gently. Keeping the key at that angle, hold the cylinder where you can and draw it out towards you, adjusting the key a little if it drags.
If it will not come: 1. Recheck that the fixing screw is completely removed and the cam is aligned, as those are the usual causes. 2. Check for a handle plate holding it and for damage or distortion to the barrel. Stop if force would be needed.
At no point should the key take a hard pull or be used as a lever. Keep the old barrel until the new one is fitted and proven.
If Any of This Applies, Stop and Call Someone
Stop here unless you have a working key and a door that opens, because every earlier step depends on both. The four stopping points are a missing key, a snapped key, a door that will not open, and a cylinder that turns but does nothing. Uncertainty counts as well: stop if the door cannot stay open and secure, the correct component is unclear, or anything requires force. That is the point where a replaceable part tends to become damage to the door, frame or entire lock.
If the Key Has Snapped, or There Is No Key
A cylinder can be removed without its key. This guide will not teach it, because instructions that open one door open them all. The outcome is what counts: the cylinder is destroyed in the process and a new one is fitted, which means the part you planned to buy is the part that goes in. A snapped key often leaves the cylinder intact once the broken section is out, so it may not need replacing.
If the Door Will Not Open or the Key Turns and Nothing Happens
Both of these are away from the barrel. A door that will not open despite a normally turning key is usually the mechanism or alignment; a handle that moves without shifting the locking points is usually the gearbox. Forcing either can break what still works.
Stop too for break-in damage, fire doors, communal or managed flat entrances, or worn parts in several places. Describe the door's state and what the key does, with photos, to.
Test the Door Before Walking Away
Before the door is closed, it gets tested open. Make that a fixed rule, because it is the step most people skip and the one that saves a lockout the next morning.
Open-door test. Insert and withdraw the key on each side, or operate the thumbturn. Lift the handle where needed, turn the key in the door's normal locking sequence, and confirm the hooks, rollers and bolts go out and come back. Follow the manufacturer's instructions if there is a trigger.
Closing test. Retract every locking point, then bring the door gently to the frame without locking. Look for a natural close and a latch that meets its keep correctly.
Closed-door test. Operate handle and key without force, from inside and then outside.
Comparing the open and closed results is the point of the exercise. If it only stiffens once closed, the barrel is not the problem; the door alignment, hinges or keeps are. Stiffness that also occurs with the door open means the cylinder's dimensions, installation and compatibility need checking again before the door is used. A replacement should operate smoothly, and a tight one is not going to wear in, so never force it. Lastly, run every key from the set through the test, on both sides.
Have It Changed Instead
If the size is unclear, the key is missing or the door is fighting you, Wilds Locksmiths Farnborough changes uPVC cylinders and mechanisms across Farnborough. The steps above are sound for a straightforward barrel; this is for the doors that are not. There is no call-out charge at any hour, emergency calls are taken 24 hours a day, every day of the year, and you are given a price on the call from what you describe.
Have ready: whether the door is uPVC or composite, whether the key turns, and a photo of the door edge and handle.
Get a Price for a uPVC Lock Change: 01252 493213
Prefer to write it down? You can book a uPVC lock change with Wilds Locksmiths Farnborough or read about our lock replacement service.
uPVC Door Lock Questions
Can I change a uPVC door lock without the original key?
A missing key usually rules out the ordinary DIY cylinder removal method. Turning a functioning key normally aligns the cam so the cylinder can come out. Professional help may therefore be needed if there is no usable key. Routine removal of the handles, cylinder and multipoint strip is normally done with the door open. A locked door is unsuitable for those replacement steps: avoid force and dismantling with locking points still secured inside the frame.
Can I change a uPVC door lock if the door will not open?
Do not attempt the normal replacement sequence on a door that is locked shut. Its handles, multipoint strip and cylinder generally come out when the door is open. For the cylinder, a key that works is normally necessary to align the cam. Without one, the standard DIY removal process is usually unsuitable and a qualified locksmith may be needed for removal. Avoid dismantling or force while locking points remain secured within 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?
Handle removal is generally unnecessary for this job. With most euro cylinders, taking out the retaining screw and turning the key to position the cam allows removal. If the cylinder is obstructed by its protective furniture or handle plates, loosening those fittings may be required.
Are all uPVC door handles the same size?
Handle sizes are not universal on uPVC doors. PZ centres and fixing positions can differ, as can the backplate's dimensions, spindle arrangement and way the handles operate. Measure the fitted set before placing an order, and consider door thickness because the required spindle and screws may need different lengths.
Why does my uPVC door lock work when open but not closed?
Closing the door may introduce resistance at the frame and locking points. That is a common explanation for this pattern. The door's position may have dropped, its hinges could be worn, or the latch and the hooks and bolts may be misaligned with the keeps.
Can I replace only the gearbox in a uPVC door lock?
Yes, a separate gearbox change is an option with a matching replacement. The locking strip connections, spindle arrangement, PZ centres, backset and fixings must each match. However, damaged or worn locking points elsewhere, or a strip in that condition, require the entire mechanism to be renewed.
Can I replace a multipoint lock with a different brand?
Yes, another brand may work if its mechanism is designed to be compatible. The gearbox, faceplate, dimensions, operating method and positions of the locking points must all suit the door. A change in locking points may also mean the frame keeps need altering.
What happens if I fit the wrong-size euro cylinder?
It may leave more cylinder exposed or make the key difficult to operate. A cylinder with excess length may show more beyond the outer protective furniture. Too short a cylinder may be set too deeply, making key operation difficult. Before ordering, measure the external side independently of the internal side.
Do I need to replace the complete lock after losing my keys?
A cylinder change will usually suffice instead of a complete lock replacement. Where the lost keys operate a euro cylinder, with every other locking component functioning correctly, renewing it should stop the keys working at the door. Also assess any additional locks with keys to establish whether they require attention.
Why is the new uPVC door handle still drooping?
Changing the handles may leave the source of the droop unresolved. Handle springs, spindle problems, fixing alignment or a fault within the gearbox may be involved. Open the door to recheck the handle sizing and fitting. Do not treat new handles as a solution to a gearbox fault.