Not every window lock works the same way. A modern uPVC casement window may have several locking points hidden along its edge, while an older timber sash window might rely on a central fastener and additional sash stops.
That difference matters when a handle breaks, a window will not lock or you need to check whether your existing security meets your home insurance requirements.
I’m Sam from AHLP Locksmiths. The first thing to establish with a faulty window is whether the problem is actually the lock. A stiff handle might be caused by poor alignment, a worn gearbox or a locking point that no longer lines up with the frame.
Replacing the handle without checking the mechanism can leave you with exactly the same problem.
This guide explains the main window lock types found in UK homes, how to identify them, what commonly goes wrong and when a repair or replacement makes sense.
Window Lock Types in the UK: Quick Comparison
The most suitable window lock depends on the frame material, opening style and existing hardware.
| Window lock type | Common window types | How it works | Typical issue |
|---|---|---|---|
| Key-locking window handle | uPVC, aluminium and some timber casements | Locks the handle against operation | Lost keys or damaged handle |
| Espagnolette (espag) lock | Modern uPVC and other casement windows | Moves locking points along the opening edge | Worn gearbox or poor alignment |
| Multipoint window lock | uPVC, aluminium and some timber systems | Secures the opening at several positions | Locking points failing to engage |
| Cockspur handle | Older uPVC and aluminium windows | Handle spur closes over a frame-mounted wedge | Incorrect replacement size or worn handle |
| Sash fastener | Traditional sliding sash windows | Secures the meeting rails together | Loose fastener or misaligned sashes |
| Sash stop | Sliding sash windows | Restricts sash movement | Missing key or damaged fitting |
| Casement window lock | Traditional timber casements | Secures the opening section to the frame | Loose fixings or damaged timber |
| Window stay lock | Timber casement windows | Locks or restricts the stay | Worn stay or damaged fitting |
| Window restrictor | Various window types | Limits opening distance | Failed or unsuitable restrictor |
One important distinction is that a key-locking handle and the internal window mechanism are often separate components.
A window can have a perfectly good handle but a faulty espagnolette mechanism behind it.
1. Key-Locking Window Handles
Key-locking handles are common on modern uPVC casement windows, although they are also fitted to some aluminium and timber windows.
The key prevents the handle from being operated, helping keep the window secured in its closed position.
On many windows, turning the handle also operates a separate locking mechanism concealed inside the opening section.
What commonly goes wrong?
A broken or loose handle does not always mean the complete window lock has failed.
Common problems include:
- Lost or damaged handle keys.
- Loose fixing screws.
- Worn or damaged spindles.
- Handles that turn without operating the mechanism.
- Handles that become stiff because the internal lock is binding.
If the handle spins freely, the spindle or internal gearbox may be damaged.
If it becomes difficult to turn only when the window is closed, poor alignment may be contributing to the problem.
Can you replace just the handle?
Often, yes.
However, the replacement must match the existing window hardware, including spindle length, fixing centres and operating arrangement.
Fitting a handle that looks similar but has the wrong dimensions may prevent the mechanism from working correctly.
2. Espagnolette Window Locks
An espagnolette lock, commonly called an espag lock, is one of the most widely used mechanisms on modern uPVC casement windows.
It is usually fitted along the edge of the opening section.
When the handle turns, the mechanism moves locking points into corresponding keeps on the frame.
These locking points may include rollers, mushroom cams or other components, depending on the design.
How do you recognise an espag lock?
Open the window and look along the edge of the opening section.
If you can see a metal strip with moving locking points, the window probably uses an espagnolette-style mechanism.
The visible handle operates this mechanism through a spindle.
Common espag lock problems
Typical faults include:
- The handle turning without moving the locking points.
- The gearbox becoming stiff or failing.
- Rollers or cams no longer engaging correctly.
- Damaged or loose keeps.
- Poor alignment between the opening section and frame.
If the mechanism works with the window open but becomes difficult when closed, alignment should be checked before replacing the lock.
A new mechanism may develop the same problem if the window remains out of adjustment.
3. Multipoint Window Locks
A multipoint window lock secures the opening section at several positions.
The term describes how the window is secured rather than identifying one particular manufacturer or mechanism.
Many espagnolette systems are multipoint arrangements because they operate several locking points along the window.
Some window systems also use additional locking components around different sides of the opening section.
Are multipoint window locks more secure?
Multiple locking points can help hold the opening section against the frame at several positions.
However, the number of locking points alone does not establish the security rating of the complete window.
The frame, glazing, hinges, keeps and correct operation of the hardware also matter.
When should a multipoint window lock be repaired?
Investigate the mechanism if the handle becomes stiff, the locking points fail to engage or the window no longer closes properly.
Do not repeatedly force the handle.
A minor alignment issue can place unnecessary strain on the gearbox and other components.
For examples of locking problems that may require repair or replacement, see our guide to lock replacement for local homes.
4. Cockspur Window Handles
Cockspur handles are commonly found on older uPVC and aluminium windows.
They are easy to recognise because the handle has a projecting nose or spur that closes over a wedge fixed to the frame.
Unlike a typical espag handle, a cockspur handle does not normally operate a concealed strip of multipoint locking hardware.
Some versions incorporate a key-operated lock.
Why cockspur replacement sizes matter
A replacement handle must match the existing window arrangement.
Important measurements include:
- The position of the fixing holes.
- The handle’s step height.
- The relationship between the spur and frame-mounted wedge.
- The handle orientation and opening direction.
A replacement with the wrong step height may not close securely against the wedge.
This is particularly important on older windows where the original hardware may no longer be readily available.
5. Sash Window Locks and Fasteners
Traditional sliding sash windows are common in older UK properties, including Victorian and Georgian-style homes.
Unlike casement windows, sash windows normally have two sections that slide vertically.
A sash fastener is typically positioned where the upper and lower meeting rails come together.
Closing the fastener secures the two sashes together.
Are traditional sash fasteners secure enough?
That depends on the product, the condition of the window and any additional security requirements.
Some traditional fasteners are relatively simple fittings, while key-locking versions offer additional control.
If the window is accessible from outside, additional suitable security hardware may be worth considering.
However, a stronger fastener cannot compensate for badly deteriorated timber or loose fixing points.
What should you check?
Look for movement in the fastener, loose screws and meeting rails that no longer align correctly.
If the sashes have shifted, the fastener may not engage properly even though the hardware itself is undamaged.
6. Sash Stops
Sash stops restrict how far a sliding sash window can open.
They are commonly used as additional security fittings on traditional sash windows.
Depending on the design and installation position, a stop can prevent the sash from moving beyond a set point.
Some sash stops are key-operated.
Are sash stops a replacement for a sash fastener?
Not necessarily.
Sash stops and sash fasteners perform different functions.
A sash fastener secures the meeting rails, while a sash stop restricts movement.
They may be used together where appropriate.
The position of the stop matters, particularly where the window has ventilation or emergency escape requirements.
7. Casement Window Locks
Traditional timber casement windows may use individual key-operated locks rather than concealed espagnolette mechanisms.
These locks secure the opening casement to the surrounding frame.
Different designs are available depending on whether the window opens outward, inward or uses particular traditional hardware.
Why timber condition matters
Before fitting a replacement lock, check the timber around the fixing points.
A strong lock fitted into weakened or rotten timber may not provide reliable security.
Also check whether the window has dropped, warped or become difficult to close.
If the lock only engages when the window is pushed firmly into position, the underlying alignment problem should be investigated.
8. Window Stay Locks
Traditional timber casement windows often have a metal stay that holds the window open at selected positions.
A window stay lock secures or restricts the stay, depending on the design.
Some versions are key-operated.
When are window stay locks useful?
They can provide additional control over traditional casement window hardware.
However, they should not automatically be treated as equivalent to a dedicated key-operated casement lock or modern multipoint system.
The correct arrangement depends on the window construction, intended use and any insurance requirements.
Check that the stay, fixings and surrounding timber are all in good condition.
9. Window Restrictors
A window restrictor limits how far a window can open.
Restrictors are used for several purposes, including controlled ventilation and reducing the risk of falls.
They are available in different forms for uPVC, timber and aluminium windows.
Are window restrictors security locks?
Not automatically.
A restrictor may limit opening distance without providing the same protection as the window’s primary locking mechanism.
Some restrictors are lockable, but their suitability depends on the product and intended purpose.
Where child safety, fall prevention or emergency escape is involved, the restrictor must be appropriate for the particular window and applicable requirements.
Never assume that fitting a generic restrictor makes an accessible window secure against forced entry.
How to Identify the Window Lock You Already Have
Before ordering replacement parts, identify the window type and the mechanism fitted.
You usually do not need to dismantle the window to make an initial assessment.
On a modern uPVC casement window
Open the window and inspect the edge of the opening section.
If there is a metal strip with moving rollers, cams or other locking points, the window probably uses an espagnolette or multipoint mechanism.
Check whether the handle operates those components smoothly.
On an older uPVC or aluminium window
Look for a handle with a projecting spur that closes over a wedge on the frame.
That usually indicates a cockspur arrangement.
The handle’s dimensions are important when choosing a replacement.
On a timber casement window
Look for separate locks securing the opening section to the frame.
Also check whether the window stay has a locking device.
Older timber windows may have several individual fittings rather than one integrated mechanism.
On a traditional sash window
Inspect the meeting rails where the upper and lower sashes overlap.
You may find a central fastener, additional locks or sash stops restricting movement.
If you are identifying a faulty component, clear photographs of the hardware and fixing positions are often more useful than a photograph of the closed window.
What Window Locks Do UK Home Insurers Require?
There is no single window lock specification required by every UK home insurance policy.
Requirements vary depending on the insurer, property and policy wording.
Some policies specify key-operated locks on ground-floor windows and other accessible windows.
Others may describe acceptable locking arrangements differently or include exceptions for particular window types.
Which windows may count as accessible?
Insurers may consider windows accessible if they can be reached from:
- Ground level.
- A flat roof.
- An extension roof.
- A balcony or external structure.
- Another readily accessible part of the building.
A first-floor window is not automatically exempt simply because it is above ground level.
The exact definition should come from your policy.
What should you check in your insurance documents?
Look for sections headed:
- Minimum security requirements.
- Door and window locks.
- Security conditions.
- Endorsements.
- Protections.
- Conditions applying when the property is unoccupied.
Check whether the policy requires locks to be fitted, operated or both.
If the wording is unclear, ask the insurer or broker to confirm which windows are covered and what type of lock is acceptable.
Can the wrong window locks affect an insurance claim?
Failing to meet an applicable security condition can create problems when making a claim.
However, whether an insurer can decline a particular claim depends on the policy wording, circumstances and applicable insurance law.
Do not assume that every burglary claim involving an unlocked or non-compliant window will automatically be rejected.
The sensible approach is to understand the security conditions before an incident occurs.
Does BS3621 Apply to Window Locks?
BS3621 is not normally the standard used to identify window locks.
It covers thief-resistant lock assemblies for doors and is commonly associated with qualifying locks fitted to timber entrance doors.
A requirement for BS3621 should therefore not automatically be interpreted as a requirement for a particular type of window lock.
If your insurance policy mentions BS3621, check which doors or locking arrangements it refers to.
For a more detailed explanation, read our guide to British Standard locks and home insurance requirements.
What Does PAS 24 Mean for Window Security?
PAS 24 is a UK security performance specification for complete doorsets and windows.
It is not a standalone grading system for an individual replacement window handle or lock.
A window assessed to PAS 24 is tested as a complete product, with the frame, glazing, locking hardware and other components contributing to its performance.
Does fitting a new window lock make a window PAS 24 compliant?
No.
Replacing an individual lock or handle does not automatically establish that the complete window meets PAS 24.
The security performance of the tested assembly depends on the components and construction covered by the relevant assessment.
If you are purchasing new windows and want a particular security specification, check the certification or test evidence for the complete window product.
If you are repairing an existing window, focus on choosing compatible hardware and restoring correct operation rather than assuming a single replacement component changes the window’s overall certification.
Which Window Locks Are Best for Ground-Floor Windows?
The best window lock is one that suits the window, operates correctly and meets any relevant insurance requirements.
| Window type | Security arrangement to consider | What to check |
|---|---|---|
| Modern uPVC casement | Properly functioning espag or multipoint system with suitable locking handle | Locking points, keeps and alignment |
| Older uPVC window | Compatible lockable cockspur handle | Step height, wedge and secure closure |
| Aluminium casement | Manufacturer-compatible locking mechanism | Hardware compatibility and frame condition |
| Timber casement | Suitable key-operated casement lock | Timber condition and fixing strength |
| Traditional sash window | Appropriate sash fastener and additional locks or stops where needed | Meeting rails, sash movement and fixings |
| Accessible upper-floor window | Suitable locking arrangement for the window | Access from roofs, balconies or other structures |
A modern multipoint mechanism is not automatically the right replacement for an older timber sash window.
Likewise, fitting an additional surface-mounted lock to a poorly aligned uPVC window may not address the actual problem.
Common Window Lock Problems and What They Mean
When a window becomes difficult to secure, the symptoms can help identify which component needs attention.
| Problem | Possible cause | What to do |
|---|---|---|
| Handle turns but locking points do not move | Worn spindle or failed gearbox | Check handle and mechanism |
| Handle is stiff when the window is closed | Poor alignment or locking points binding | Check keeps and alignment |
| Window closes but will not lock | Misaligned hardware or damaged mechanism | Identify the fault before replacing parts |
| Key will not turn in the handle | Damaged key or handle cylinder | Assess whether the handle needs replacing |
| Cockspur handle will not catch the wedge | Incorrect positioning, wear or damage | Check dimensions and fittings |
| Sash fastener will not engage | Misaligned sashes or loose fixings | Check window movement and timber condition |
| Window lock is loose | Worn fixings or damaged frame material | Repair the fixing point before refitting |
| Restrictor no longer holds | Damaged or unsuitable restrictor | Replace with a compatible product |
These are possible causes rather than definitive diagnoses.
A locksmith should establish the fault before recommending replacement parts.
Can You Replace a Window Lock Without Replacing the Whole Window?
In many cases, yes.
Window handles, espagnolette mechanisms, cockspur fittings, sash fasteners and other individual components can often be replaced where suitable parts are available.
The main difficulty is identifying the correct replacement.
What makes older window locks harder to replace?
Manufacturers change designs and dimensions over time.
An older espag mechanism may have a particular backset, faceplate width, gearbox position or locking-point arrangement that needs to be matched.
Similarly, a cockspur handle may look almost identical to a replacement but have a different step height.
A part that does not fit correctly can prevent the window from locking securely.
When might the whole window need attention?
If the frame is badly damaged, the opening section is distorted or the surrounding material can no longer support the locking hardware, changing the lock alone may not solve the problem.
The window should be assessed as a complete assembly.
When Should You Repair or Upgrade Your Window Locks?
Consider a professional assessment when:
- A window cannot be secured reliably.
- The handle spins or no longer operates the mechanism.
- The locking points fail to engage.
- The window needs excessive force to close.
- Keys have been lost.
- The hardware is damaged or corroded.
- The frame or fixing points are deteriorating.
- You are unsure whether accessible windows meet your insurance requirements.
- There are signs of attempted forced entry.
Not every older lock needs replacing.
If the existing hardware is suitable and working correctly, replacement may provide little practical benefit.
Where a fault exists, identifying whether it involves the handle, mechanism or alignment can prevent unnecessary expense.
Sam’s Advice: Check the Mechanism Before Buying a New Handle
If a uPVC window will not lock, do not assume the handle is the problem.
Open the window, where it is safe to do so, and check whether the handle moves the locking points along the edge.
If the mechanism works normally when open but becomes stiff when closed, the issue may involve alignment rather than a broken lock.
If the handle turns but the locking points do not move, the spindle or gearbox may have failed.
For older cockspur and sash window fittings, identify the exact dimensions and fixing arrangement before buying replacement hardware.
The aim is to repair the actual fault, not replace parts through guesswork.
Window Lock Repairs and Security Advice in Bristol
A window that will not lock properly should not be ignored, particularly if it is accessible from outside.
AHLP Locksmiths can help identify suitable lock repairs and replacement options for residential properties across Bristol, South Gloucestershire and Gloucester.
If you are unsure what type of window lock is fitted, take photographs of the handle, opening edge and visible locking components where possible.
You can explore AHLP’s locksmith services for further information about lock repairs and security improvements.
For a wider review of doors, windows, side access and other entry points, read our home security advice for Bristol and South Gloucestershire.
Frequently Asked Questions
What are the main types of window locks in UK homes?
Common UK window lock types include key-locking handles, espagnolette mechanisms, multipoint locks, cockspur handles, sash fasteners, sash stops and separate casement locks. Window stay locks are also found on traditional timber casements, while restrictors limit how far a window can open. Different mechanisms suit different window constructions and opening styles. Identifying whether your window is uPVC, aluminium, timber, casement or sliding sash is the best starting point.
What type of lock is fitted to a uPVC window?
Most modern uPVC casement windows use an espagnolette or multipoint locking mechanism operated by a handle. The mechanism moves locking points into keeps positioned around the frame, while the handle itself may also be key lockable. Older uPVC windows sometimes use cockspur handles that close over a wedge on the frame. If the window will not lock, check whether the fault is in the handle, mechanism or alignment before replacing anything.
Do ground-floor windows need key-operated locks for home insurance?
Some UK home insurance policies require key-operated locks on ground-floor and other accessible windows, but the requirements are not universal. Your policy may also specify security for windows reachable from flat roofs, balconies or extensions. Check the exact wording in the security conditions and endorsements before buying new locks. If you are unsure which windows are covered, ask your insurer or broker to confirm the requirements.
Are multipoint window locks better than single-point locks?
Multipoint locks secure a window at several positions, which can help hold the opening section against the frame. However, the number of locking points alone does not determine the security of the complete window. The quality of the frame, hinges, glazing and hardware installation also matters. The best arrangement is one that is compatible with the window and meets any relevant security requirements.
What is the difference between an espag lock and a cockspur handle?
An espagnolette lock is a mechanism that operates locking points along the edge of a window, usually through a separate handle. A cockspur handle has a projecting spur that closes over a wedge fitted to the frame. Espag systems are common on modern uPVC windows, while cockspur handles are frequently found on older uPVC and aluminium windows. Their replacement parts are not interchangeable, so the existing hardware must be identified correctly.
Are sash window locks suitable for older timber windows?
Yes, suitable sash fasteners and additional locking devices can improve security on traditional sliding sash windows. The correct arrangement depends on the condition of the timber, alignment of the sashes and how the window is used. Key-locking fasteners and sash stops may be appropriate in some situations. Any additional hardware should be installed without damaging the window or interfering with necessary opening arrangements.
Does PAS 24 apply to individual window locks?
PAS 24 assesses the security performance of complete doorsets and windows rather than individual replacement window locks. The frame, glazing, locking system and other components contribute to the tested assembly’s performance. Installing a new handle or lock does not automatically make an existing window PAS 24 compliant. If you need PAS 24 security performance, check the evidence for the complete window product.
Does BS3621 apply to window locks?
BS3621 is a standard for thief-resistant lock assemblies used on doors, not the usual standard for residential window locks. It is commonly associated with qualifying locks fitted to timber entrance doors. Window security requirements are normally considered separately under the relevant insurance policy and product specifications. If your insurer mentions BS3621, confirm which doors or locking arrangements the requirement applies to.
Can a locksmith replace a broken window lock without replacing the window?
In many cases, a locksmith can replace a faulty handle, espagnolette mechanism, cockspur fitting or sash lock without changing the complete window. The replacement must match the existing hardware and fit the window correctly. Older mechanisms may be harder to source, although compatible alternatives are sometimes available. If the frame or opening section is badly damaged, additional repairs may be needed.
Why does my window handle turn but the window will not lock?
A handle that turns without operating the locking points may indicate a worn spindle or failed gearbox. If the mechanism moves but does not engage when the window closes, alignment or damaged keeps may be the cause. Forcing the handle can make an existing fault worse. The handle, mechanism and frame should be checked together before choosing replacement parts.
Are window restrictors the same as security locks?
No, window restrictors primarily control how far a window can open. Some are lockable, but that does not automatically mean they provide the same security as the window’s main locking mechanism. Restrictors may be installed for ventilation or fall-prevention purposes, depending on the window and setting. The correct product must account for safety and any applicable emergency escape requirements.
When should I replace my window locks?
Replacement is worth considering when a window cannot be secured properly, the hardware is damaged or the existing arrangement does not meet a relevant security requirement. Lost keys, failed gearboxes, broken handles and worn fittings can also justify replacement. However, a stiff handle may be caused by alignment rather than a faulty lock. Identifying the underlying problem first can avoid replacing parts unnecessarily.