uPVC Gearbox Replacement: Signs, Sizes & Repair Options
A uPVC door handle that won't lift, a key that refuses to turn or a door that won't lock can point to a faulty gearbox. But the gearbox isn't always the problem.
This guide explains what a uPVC door lock gearbox does, how to recognise common faults, what measurements matter when choosing a replacement and when a locksmith should inspect the complete locking mechanism.
Quick answer: what is a uPVC gearbox?
A uPVC door gearbox is the central operating case in many multipoint locking systems. It connects the handle and key-operated cylinder to the locking mechanism, allowing hooks, rollers or bolts along the door edge to engage and release.
If the gearbox fails, the handle may become floppy, refuse to lift or stop operating the locking points. In some cases only the central gearbox needs replacing; in others, the full multipoint lock strip or another component requires attention.
What does a uPVC door gearbox actually do?
Most modern uPVC entrance doors use a multipoint locking mechanism. Instead of securing the door at only one point, the system can operate several locking points along the door edge.
The gearbox is the central case where the handle spindle and euro cylinder interact with the mechanism.
Door handle and spindle
The handle turns a metal spindle passing into the gearbox. On many lift-to-lock doors, lifting the handle operates the locking points.
Central gearbox
The gearbox contains internal moving parts that transfer movement from the handle and key to the lock mechanism.
Multipoint locking strip
The strip runs along the door edge and operates hooks, rollers, bolts or other locking points, depending on the system.
Gearbox versus complete mechanism: The gearbox is one component of the system. Replacing the centre case is not the same as replacing the entire multipoint locking strip.
This distinction matters because a compatible centre case may allow a more targeted repair, while damaged connecting rods, locking points or an obsolete mechanism may require a complete replacement.
For a broader explanation of the system, see our uPVC door lock mechanism guide.
Signs your uPVC door gearbox may be faulty
A gearbox can wear internally, but similar symptoms can also come from the handle, cylinder, door alignment or other locking components.
Handle spins or feels floppy
A failed internal component, worn spindle connection or broken handle spring can cause lost movement. The handle assembly needs checking before blaming the gearbox.
Handle won't lift fully
The locking points may be obstructed, the door may have dropped, or the gearbox may be binding internally.
Key won't turn to lock
If the handle has not fully engaged the mechanism, the cylinder may not complete its turn. Cylinder faults can produce similar symptoms.
Grinding or clicking noises
Unusual noises can indicate worn or damaged moving parts, although the exact source needs inspection.
Handle moves but nothing happens
A disconnected or damaged internal drive may stop the gearbox transferring movement to the locking points.
Door becomes difficult to secure
A previously smooth locking action becoming increasingly stiff can indicate alignment problems or wear within the mechanism.
Do not force the handle or key. Excessive force can damage the cylinder, handle, gearbox or other parts of the multipoint system. If the door is stuck closed, seek professional assistance rather than dismantling the lock.
Is it the gearbox, the handle or the door alignment?
The most useful first step is identifying whether the mechanism operates differently when the door is open compared with when it is closed.
| What you notice | Possible cause | Recommended next step |
|---|---|---|
| Handle lifts normally with the door open but struggles when closed | Door misalignment, keeps or compression pressure | Check door alignment before replacing the gearbox. |
| Handle remains stiff even with the door open | Gearbox, handle or multipoint mechanism fault | Stop forcing it and arrange diagnosis. |
| Handle droops but the door still locks | Handle spring cassette or return spring issue | Inspect the handle assembly and gearbox spring arrangement. |
| Handle turns without operating the lock | Worn spindle, handle connection or internal gearbox damage | Inspect the drive connection and centre case. |
| Key is difficult to insert or turn independently of the handle | Possible cylinder or key problem | Check the cylinder before replacing the gearbox. |
| Hooks or bolts fail to retract correctly | Gearbox or another part of the multipoint strip | Inspect the full mechanism, not just the centre case. |
A cautious open-door check
If the door is already open and the mechanism moves freely, you can compare how the handle feels with the door open and closed. Keep the door supported and ensure any projected hooks or bolts are retracted before attempting to close it.
If the handle operates smoothly while open but binds when closed, the door's alignment or keeps may be responsible. If the mechanism is stiff in both positions, an internal fault becomes more plausible.
Safety: Do not perform this check if the mechanism is already jammed, the door is your only safe exit, or you cannot reliably retract the locking points. Do not close the door with the bolts extended.
If your uPVC door won't lock and you're unsure whether the problem is the gearbox, handle or alignment, read our uPVC door won't lock troubleshooting guide to understand the possible causes.
For problems caused by a dropped or poorly aligned door, read our uPVC door adjustment guide.
How to measure a uPVC gearbox correctly
Not all multipoint gearboxes are interchangeable. Two centre cases may look similar but use different dimensions, spindle arrangements or connections to the locking strip.
These are the main measurements and details to identify before ordering a replacement.
1. Backset measurement
The backset is the distance from the front edge of the lock faceplate to the centre of the handle spindle hole.
Common sizes include 35mm and 45mm, but other dimensions exist. Measure the existing unit rather than assuming.
2. PZ measurement
PZ is the centre-to-centre distance between the handle spindle and the euro cylinder keyhole position.
A 92mm PZ is common on many uPVC doors, but 70mm, 68mm and other arrangements are also found. Some gearboxes have more than one spindle position.
3. Gearbox case dimensions
The height, width and thickness of the central case may affect whether the replacement fits into the door.
4. Faceplate and connection details
Check the faceplate width, fixing points, attachment style and how the gearbox connects to the rest of the locking strip.
Before ordering: Record the manufacturer's markings, existing measurements, spindle arrangement, latch direction and any model or part number visible on the mechanism.
Gearbox identification checklist
- Manufacturer name or stamped markings
- Backset measurement in millimetres
- PZ measurement or measurements
- Single, split or dual-spindle arrangement
- Centre-case height, width and thickness
- Faceplate and fixing configuration
- Latch, deadbolt and follower arrangement
- Connection to the existing multipoint strip
If the mechanism is still fitted, photos of the faceplate, handle and visible markings may help a locksmith narrow down the options. Internal dimensions may still require inspection after safe removal.
Different types of multipoint lock gearboxes
The correct replacement depends on more than the brand printed on the faceplate. Spindle operation, case geometry and strip connections must match the existing mechanism.
Single-spindle gearbox
Uses one handle spindle position. Common on lever-operated multipoint doors, although the precise operation varies by model.
Split-spindle gearbox
Can provide different inside and outside handle functions. It must be matched to the intended handle and locking operation.
Dual-spindle gearbox
Has two follower positions on some systems. Both measurements and operating behaviour must be checked before replacement.
Does the gearbox brand matter?
Yes. Common multipoint lock manufacturers include ERA, GU, Fuhr, Mila, Maco, Winkhaus and Yale, among others. However, a manufacturer's name alone does not identify the correct replacement.
Models within the same brand can differ significantly. Some older mechanisms also require an approved alternative or complete replacement strip if an exact centre case is unavailable.
Compatibility warning: A gearbox with the correct PZ and backset is not necessarily compatible. The fixing points, case dimensions, follower operation and connection to the locking strip must also match.
How is a uPVC door gearbox replaced?
Replacing a gearbox is a mechanical repair that usually involves removing the door furniture, cylinder and multipoint locking strip to access the central case.
The exact procedure varies by manufacturer. The outline below explains what a suitable repair normally involves, rather than providing a universal dismantling method.
Confirm the actual fault
The handle, cylinder, alignment and locking points are assessed to establish whether the gearbox is the cause.
Identify the existing mechanism
Manufacturer markings, dimensions and spindle configuration are recorded to select a compatible replacement.
Remove the mechanism safely
With the door safely open, the relevant fittings and multipoint strip are removed according to the manufacturer's arrangement.
Replace the central case
If the gearbox is a separately replaceable component, the compatible unit is fitted and correctly connected to the strip.
Reassemble and test
The handle, cylinder, latch and locking points are checked while the door remains open. Operation is then checked against the frame without forcing the mechanism.
Check alignment and closing pressure
Where needed, door alignment and keeps are assessed so the repaired mechanism is not subjected to the same excessive resistance.
Can you replace it yourself? A competent DIYer may be able to replace a clearly identified, accessible gearbox on an open door. However, a jammed door, uncertain compatibility or damaged multipoint strip is better handled by a locksmith. Incorrect reassembly can leave the door insecure or unable to open.
Gearbox replacement or complete multipoint lock replacement?
A centre-case replacement can be appropriate when the fault is confined to the gearbox and the remaining mechanism is in serviceable condition.
Replacing the complete strip may be more sensible if multiple components are damaged, the mechanism is heavily worn or a compatible gearbox is not available.
Gearbox-only replacement
Potentially suitable when:
- The central gearbox is confirmed faulty.
- The rest of the locking strip works correctly.
- A compatible replacement case is available.
- Connecting components are undamaged.
- The door can be aligned and tested properly.
Benefit: Retains serviceable components and may reduce parts and labour costs.
Full multipoint mechanism replacement
May be required when:
- The locking strip is bent or damaged.
- Hooks, rollers or connecting rods have failed.
- The centre case is not separately replaceable.
- The original mechanism is obsolete.
- Wear affects several parts of the system.
Benefit: Addresses faults across the complete mechanism rather than replacing one component.
If your door is difficult to lock but the gearbox is working, a door adjustment may be more appropriate than replacing either component.
How much does uPVC gearbox replacement cost?
The cost depends on the mechanism, availability of compatible parts, whether the door is stuck shut, and how much work is required to remove, fit and test the replacement.
A gearbox-only repair may cost less than replacing a complete multipoint locking strip, but that is not guaranteed. Some replacement centre cases are harder to source, and opening a jammed door can add labour.
| Cost factor | Why it affects the quote |
|---|---|
| Gearbox make and model | Parts vary in availability and price. |
| Gearbox-only or complete strip | A full multipoint mechanism generally involves more hardware. |
| Door open or jammed shut | Accessing a seized mechanism can require additional work. |
| Door alignment | Adjustment may be needed to prevent repeated strain. |
| Handle or cylinder condition | Other worn components may need separate attention. |
| Appointment circumstances | Attendance arrangements and out-of-hours work can affect pricing. |
Lock Luxe pricing information
Lock Luxe currently advertises uPVC mechanism work from £149, with a £49 attendance charge listed separately. These are published starting figures, not a guaranteed price for an individual gearbox replacement.
The final quote should establish the required part, labour, attendance charges and any additional work before the repair is agreed.
How to reduce wear on a uPVC door gearbox
Multipoint gearboxes are mechanical components. Wear cannot be eliminated, but unnecessary strain can often be reduced.
Address door misalignment
If the door catches the frame or requires lifting to close, investigate alignment before the locking mechanism is placed under further strain.
Don't force the handle
A handle that suddenly needs extra force is a warning sign. Repeatedly forcing it can damage internal components.
Keep the mechanism clean
Remove accessible dirt and debris around the door edge and keeps. Use only cleaning or lubrication products appropriate to the specific mechanism.
Check closing pressure
Weather seals, keeps and door positioning can affect how easily the locking points engage.
Investigate unusual sounds
Grinding, clicking or sudden changes in handle movement deserve attention before the mechanism becomes completely jammed.
Use compatible replacement parts
Incorrect handles, spindles or gearboxes can create operational problems even if they appear to fit initially.
uPVC gearbox replacement FAQs
Answers to common questions about failed gearboxes, multipoint mechanisms and replacement parts.
Can you replace just the gearbox on a uPVC door?
Yes, on many multipoint systems the central gearbox can be replaced separately. However, the correct part must be available and compatible, and the rest of the locking strip must be in suitable condition. Some mechanisms require complete replacement.
How do I know if my uPVC gearbox is broken?
Possible signs include a handle that spins without operating the locking points, a handle that won't lift, internal grinding or a mechanism that remains stiff with the door open. These symptoms are not conclusive, so the handle, cylinder and door alignment should also be checked.
Why won't my uPVC door handle lift?
The locking points may be obstructed by misalignment, the handle or spindle may be damaged, or the gearbox may have failed. If the handle works normally with the door open but not closed, alignment is a strong possibility.
What is the difference between a gearbox and a multipoint lock?
The gearbox is the central operating case. The complete multipoint lock includes the centre case, connecting components and additional locking points positioned along the door edge.
What does 35mm backset and 92mm PZ mean?
A 35mm backset means the distance from the faceplate front to the spindle centre is 35mm. A 92mm PZ means the spindle centre and cylinder centre are 92mm apart. Other sizes exist, and these measurements alone do not guarantee compatibility.
Can a faulty gearbox stop the door from opening?
Yes. Internal damage may prevent the latch or multipoint locking components from retracting. However, a jammed locking strip, handle problem or other obstruction can cause similar symptoms. Avoid forcing the door or dismantling a mechanism while it is locked shut.
How long does a uPVC gearbox replacement take?
There is no reliable universal time. An accessible, compatible centre-case replacement can be relatively straightforward, while a jammed door, obsolete mechanism or additional alignment work can take longer. The locksmith should assess the job before estimating the work involved.
Can I fit a different brand of gearbox?
Sometimes a compatible alternative is available, but matching the backset and PZ is not enough. The gearbox must also suit the spindle operation, fixing points, dimensions and connection to the multipoint strip.
Should I replace the whole door if the gearbox breaks?
Usually a gearbox fault does not automatically mean the entire door needs replacing. The lock mechanism or relevant components can often be repaired or replaced, provided the door itself remains serviceable.
Is a floppy handle always a gearbox fault?
No. A floppy handle can result from a broken return spring, worn handle assembly, loose fixings, spindle problems or internal gearbox damage. The actual cause should be identified before buying parts.
Need help with a faulty uPVC gearbox?
If your uPVC door won't lock, the handle has stopped operating the mechanism or you're unsure which replacement gearbox is needed, Lock Luxe can discuss the problem and the appropriate next step.
Based in Hendon, Lock Luxe serves surrounding areas including Finchley, Golders Green, Mill Hill, Colindale, Edgware and nearby North West London locations.
What to tell us
1. Does the door open and close?
2. Does the handle lift or turn?
3. Does the key turn normally?
4. Does the problem happen with the door open?
5. Can you photograph the handle, door edge and manufacturer markings?