Contents
- Why Correct Diagnosis Matters
- How Modern Doors Fail
- Fault Finder by Symptom
- Locking Problems
- Handle Problems
- Key Problems
- Alignment Problems
- Mechanism Problems
- Security Problems
- Seasonal Problems
- French Door Problems
- Conservatory Door Problems
- When Is It an Emergency?
- Repair or Replace?
- Frequently Asked Questions
- Conclusion
Introduction
When a door develops a fault, the symptom you notice isn't necessarily the component that has failed.
A key that won't turn could indicate a faulty cylinder, but it could also be caused by a gearbox under load or a door that has moved out of alignment.
A handle that won't lift could be a failed gearbox, but it could equally be caused by excessive resistance from the locking points, a problem with the keeps or a door that has dropped.
A door that suddenly becomes difficult to lock therefore shouldn't automatically be treated as a failed lock.
Modern uPVC and composite doors are mechanical systems containing multiple components that have to work together.
The:
Handle → spindle → gearbox → mechanism → locking points → keeps → frame
all have to operate together correctly.
This guide explains how to diagnose the most common door problems, what the symptoms can indicate and why identifying the underlying cause is often more important than simply replacing a component.
Why Correct Diagnosis Matters
The most important part of repairing a door is identifying what has actually gone wrong.
A symptom tells you that something isn't operating correctly.
It doesn't necessarily tell you why.
For example:
Symptom: Key won't turn.
Possible causes:
- Faulty euro cylinder
- Gearbox problem
- Door alignment
- Locking point binding
- Excessive seal pressure
Replacing the cylinder without checking the rest of the system could therefore fail to solve the problem.
Symptoms vs Causes
This distinction is particularly important with multipoint locking systems.
A component may be showing the symptom while another component is creating the problem.
For example, a gearbox may eventually fail because it has been operating against excessive resistance for months.
The gearbox is what has failed.
But poor alignment may have been the original cause.
Why Guessing Can Cost More
Replacing parts based solely on symptoms can result in unnecessary work.
A homeowner may be told they need:
- A new gearbox
- A new mechanism
- New handles
- A new cylinder
- Even a complete door
when the actual problem may be a relatively simple alignment fault.
Conversely, repeatedly adjusting a door when the gearbox is genuinely damaged won't repair the underlying mechanical failure.
Good diagnosis therefore involves examining the complete system.
How Modern Doors Fail
Door faults generally develop through a combination of wear, movement, friction and repeated mechanical loading.
A typical multipoint locking mechanism may operate thousands of times during its service life.
Every operation places some load on:
- Handle
- Spindle
- Gearbox
- Drive rails
- Locking points
- Keeps
- Hinges
Under normal conditions, these components should operate with relatively little resistance.
Problems begin when that resistance increases.
Progressive Wear
Wear rarely appears all at once.
A mechanism may initially feel completely normal.
Over time:
- A hinge develops slight movement.
- The door position changes.
- Locking points begin contacting the keeps differently.
- Friction increases.
- The handle becomes slightly heavier.
- More force is applied.
- Internal components experience greater loading.
- Wear accelerates.
- Eventually something fails.
The final failure can appear sudden even though the underlying problem has been developing for a long time.
Alignment Changes
Doors and buildings move.
Hinges can wear.
Fixings can loosen.
Weather seals can change shape.
Frames can move.
All of these can alter the relationship between the door and frame.
Because multipoint locks operate using several locking points, relatively small changes can have a noticeable effect.
Friction
Friction is particularly important.
A locking point that moves freely into its keep places relatively little load on the gearbox.
A locking point that strikes or rubs against its keep requires considerably more force.
That force is transmitted back through the mechanism.
The user then compensates by pushing, pulling or lifting the handle harder.
This increases the load on the gearbox.
Gearbox Overload
The gearbox is often blamed when a multipoint door fails.
Sometimes it genuinely is the original fault.
But sometimes the gearbox is simply the component that eventually gives up after operating under excessive load.
This is why replacing the gearbox without checking alignment can result in another failure.
A replacement component cannot correct an underlying mechanical problem elsewhere in the door.
Fault Finder by Symptom
| Symptom | Possible Causes |
|---|---|
| Handle won't lift | Gearbox, alignment, locking points |
| Handle won't return | Handle springs, spring cassette, mechanism |
| Key won't turn | Cylinder, gearbox, alignment |
| Key is stiff | Cylinder, alignment, locking pressure |
| Door needs lifting | Hinge movement, alignment |
| Handles droop | Handle springs, spring cassette |
| Door catches frame | Alignment, hinges, frame movement |
| Door is jammed | Gearbox, locking points, mechanism |
| Door locks when open only | Alignment, keeps, compression |
| Key difficult to remove | Cylinder or incorrect alignment |
| Handle feels heavy | Alignment, friction, gearbox |
| Door won't deadlock | Gearbox, cylinder, mechanism |
| Lock works one way only | Cylinder, gearbox or mechanism |
| Door rattles | Keeps, compression, seals |
| Grinding noise | Locking points contacting keeps |
This table is a starting point rather than a definitive diagnosis. Several faults can produce the same symptom.
Locking Problems
Door Won't Lock
Possible causes include:
- Failed gearbox
- Misaligned locking points
- Door dropped
- Incorrect keep position
- Faulty cylinder
- Seized locking point
- Excessive seal pressure
The first question should be whether the mechanism operates normally with the door open.
If it does, the interaction between the door and frame needs investigation.
Door Won't Unlock
A door that won't unlock can be more complicated.
Possible causes include:
- Failed gearbox
- Broken internal component
- Faulty cylinder
- Jammed locking point
- Door under excessive pressure
- Misalignment
Forcing the handle or key can make the situation worse.
Door Locks Open but Not Closed
This is an important diagnostic clue.
If the locking mechanism operates correctly while the door is open but won't lock once the door is closed, the frame and locking points should be investigated.
Possible causes include:
- Door alignment
- Dropped door
- Incorrect keeps
- Excessive seal compression
- Locking point interference
Door Won't Deadlock
If the latch operates but the deadbolt or other locking points won't fully engage, the problem could be inside the mechanism or caused by the locking points not reaching their correct position.
The cylinder, gearbox and mechanism should be assessed together.
Lock Feels Stiff
A stiff lock isn't automatically a bad cylinder.
Potential causes include:
- Cylinder wear
- Door alignment
- Excessive compression
- Locking points rubbing
- Gearbox wear
- Seized components
A cylinder that turns freely with the door open but becomes difficult when closed is particularly suggestive of a mechanical or alignment problem elsewhere.
Handle Problems
Handle Won't Lift
On a lift-to-lock multipoint system, the handle has to move the locking mechanism through its complete operating cycle.
If it suddenly becomes difficult or impossible to lift, possible causes include:
- Gearbox failure
- Door alignment
- Locking points binding
- Seized mechanism
- Damaged handle
- Internal obstruction
Handle Won't Go Down
A handle that won't return can indicate:
- Gearbox failure
- Broken spring
- Spring cassette failure
- Locking mechanism problem
- Excessive friction
Loose Handle
A loose handle may simply have loose fixing screws.
However, it can also indicate:
- Worn handle
- Damaged backplate
- Worn spindle
- Worn follower
- Internal handle failure
The fix should address the reason the handle became loose rather than simply tightening it repeatedly.
Drooping Handles
Handles should normally return to their intended position after operation.
Drooping can be caused by:
- Failed handle springs
- Failed spring cassette
- Excessive gearbox resistance
- Worn mechanism
If new handles are fitted to a mechanism that is already operating under excessive resistance, they may eventually develop the same problem.
Broken Handle
A broken handle normally requires replacement.
However, the mechanism should still be checked.
If the original handle failed because the gearbox or locking points were unusually stiff, replacing the handle alone may only temporarily solve the problem.
Key Problems
Key Difficult to Turn
Possible causes include:
- Worn cylinder
- Door alignment
- Gearbox resistance
- Locking point friction
- Excessive compression
The relationship between the key, cylinder and gearbox needs to be considered.
Key Difficult to Remove
A key that won't easily return to its normal position can indicate that the cylinder isn't reaching its correct rotational position.
Possible causes include:
- Cylinder wear
- Gearbox resistance
- Misalignment
- Locking pressure
Key Has Snapped
A snapped key can result from:
- Worn key
- Poor-quality key copy
- Excessive force
- Stiff cylinder
- Locking mechanism under load
If a key repeatedly becomes difficult to turn, replacing the key alone doesn't address the underlying problem.
Key Spins
If the key turns without operating the lock correctly, possible causes include:
- Cylinder failure
- Broken cam
- Gearbox failure
- Internal mechanism damage
The exact cause depends on the locking system.
Wrong or Poorly Cut Keys
Not every key problem is caused by the lock.
Poorly cut duplicate keys can create:
- Stiff operation
- Difficulty entering the cylinder
- Difficulty turning
- Difficulty removing the key
A quality replacement key should be cut accurately for the particular lock.
Alignment Problems
Door Has Dropped
One of the most common complaints is:
"I have to lift the door to lock it."
This can indicate that the locking edge has moved downward relative to the frame.
Potential causes include:
- Hinge movement
- Door weight
- Loose fixings
- Hinge wear
- Building movement
- Structural movement
Door Catches the Frame
If the door catches against the frame, it may have moved relative to the opening.
This can affect both operation and locking.
The hinges, frame, door gaps and locking points should be considered together.
Uneven Gaps
The gap between the door and frame provides useful information.
Large differences from one area to another can indicate movement or incorrect positioning.
The important thing isn't simply making the gap visually even.
The door also needs to sit correctly relative to:
- Hinges
- Seals
- Keeps
- Locking points
Grinding or Rubbing
Grinding noises are a warning that components may be contacting each other where they shouldn't.
Potential sources include:
- Hooks
- Rollers
- Mushroom cams
- Shoot bolts
- Keeps
- Faceplates
- Hinges
Continuing to operate a mechanism under these conditions can increase wear.
Mechanism Problems
The locking mechanism is the complete assembly installed into the door.
Depending on the design it can include:
- Gearbox
- Drive rails
- Hooks
- Rollers
- Deadbolts
- Shoot bolts
- Latch
- Locking cams
Gearbox Failure
A gearbox can fail internally through:
- Wear
- Broken gears
- Broken springs
- Internal component failure
- Excessive loading
A failed gearbox may produce symptoms such as:
- Handle won't lift
- Handle spins
- Handle won't return
- Door won't lock
- Door won't unlock
The gearbox isn't necessarily the entire mechanism.
On many doors it can be replaced separately.
Broken Hooks
Hooks are locking points designed to engage with corresponding keeps in the frame.
A broken or seized hook can prevent the mechanism from operating correctly.
The cause should still be investigated.
A hook damaged because it repeatedly struck an incorrectly positioned keep represents a different problem from a hook that simply failed through internal wear.
Seized Rollers
Rollers provide a locking and compression function on many multipoint mechanisms.
If they seize or become excessively stiff, they can increase resistance throughout the mechanism.
Broken Springs
Springs are used in several areas of door hardware.
A failed spring can affect:
- Handle return
- Latch operation
- Gearbox operation
- Locking points
The exact symptom depends on which spring has failed.
Failed Latch
The latch holds the door closed when the locking system isn't fully engaged.
A faulty latch can cause:
- Door not catching
- Door bouncing open
- Difficulty closing
- Handle problems
Obsolete Mechanisms
Older doors can contain mechanisms that are no longer manufactured.
Obsolete does not automatically mean the door needs replacing.
Depending on the design, it may be possible to:
- Repair the existing mechanism
- Replace individual components
- Adapt a newer mechanism
- Upgrade the locking system
The feasibility depends on the door, mechanism and available replacement components.
Security Problems
Security problems aren't always caused by an obvious break-in.
Hardware can be poorly specified or incorrectly installed.
Potential issues include:
- Excessively projecting cylinder
- Standard cylinder with inadequate attack resistance
- Damaged cylinder
- Weak or damaged handles
- Poorly secured keeps
- Inadequate fixings
Cylinder Projection
A euro cylinder should be correctly sized for the door and hardware.
Excessive projection can increase its exposure to physical attack.
This is one reason accurate cylinder measurement matters.
Standard vs Security Cylinders
Modern security cylinders can incorporate features designed to resist common forms of attack, including:
- Snapping
- Drilling
- Picking
- Bumping
The exact protection depends on the particular cylinder.
Upgrading the cylinder can sometimes significantly improve security without replacing the entire locking mechanism.
Seasonal Problems
Some door problems appear at particular times of the year.
This isn't necessarily coincidence.
Summer
Heat and direct sunlight can cause materials to expand.
South-facing doors can be particularly exposed to solar heating.
Symptoms may include:
- Stiff handles
- Difficult keys
- Increased compression
- Door catching
Winter
Cold temperatures can cause contraction in some materials.
Changes in weather can also affect moisture content and building conditions.
A door that behaves differently in winter and summer may therefore need to be assessed for movement rather than simply having its lock replaced.
Conservatory Doors
Conservatory doors can experience significant environmental changes.
Large glazed areas can result in substantial temperature differences between the conservatory and outside environment.
This can contribute to:
- Thermal movement
- Alignment changes
- Seal compression changes
- Locking difficulties
House Movement
The door isn't isolated from the building.
Movement in:
- Foundations
- Frames
- Extensions
- Timber structures
- Masonry
can alter the position of the doorway.
This is particularly relevant where a door repeatedly goes out of alignment after being adjusted.
If the same problem keeps returning, the underlying structural or installation conditions may need to be considered.
French Door Problems
French doors introduce additional complexity because two door leaves have to work together.
One door is often the active leaf, while the other is the passive leaf.
The passive door can incorporate:
- Shoot bolts
- Keeps
- Centre locking arrangements
Problems can occur when:
- The two doors move against each other
- The centre gap changes
- Shoot bolts become misaligned
- The passive leaf isn't correctly secured
- Hinges move
A small alignment issue can therefore affect both doors.
Conservatory Door Problems
Conservatory doors can develop many of the same problems as other uPVC and composite doors.
Common complaints include:
- Door won't lock
- Handle becomes stiff
- Key becomes difficult
- Door needs lifting
- Lock works differently depending on temperature
Because conservatories can experience significant temperature changes, alignment and thermal movement should be considered alongside normal hardware wear.
When Is It an Emergency?
Some door faults require immediate attention.
Door Jammed Shut
A failed gearbox or mechanism can leave occupants unable to access or exit through the door.
Door Won't Secure
A door that cannot be locked may leave the property vulnerable.
Lock Damaged Following Forced Entry
Damage caused by attempted entry should be assessed for both mechanical operation and security.
Key Snapped Inside
A broken key can prevent normal operation and may require removal before the lock can be used.
Mechanism Failed Open
If the locking system has failed and the door cannot be secured, it should be dealt with promptly.
Repair or Replace?
The correct solution depends on what has actually failed.
Gearbox Only
If the gearbox has failed and the rest of the mechanism is sound, replacing the gearbox may be sufficient.
Handles
If the handles are worn or broken but the locking system is healthy, the handles may be replaced independently.
Cylinder
A worn or inadequate euro cylinder can usually be replaced without replacing the complete mechanism.
Mechanism
If multiple parts are damaged or the mechanism is beyond economical repair, replacing the complete mechanism may be appropriate.
Complete Door
A new door should generally be considered when the door itself is structurally unsuitable, severely damaged or no longer economically repairable.
A failed lock does not automatically mean a failed door.
Frequently Asked Questions
Why won't my uPVC door lock?
Possible causes include alignment problems, a failed gearbox, damaged locking points, a faulty cylinder or excessive compression.
Why won't my uPVC door unlock?
A failed gearbox, cylinder or locking mechanism can prevent unlocking. Pressure caused by misalignment can also contribute.
Why do I need to lift the door to lock it?
This commonly indicates that the door has moved downward relative to the frame, although the exact cause needs to be established.
Why is my key stiff?
A stiff key can be caused by the cylinder itself, but also by alignment, locking-point resistance or gearbox problems.
Can a gearbox be repaired?
Some gearboxes can be repaired, but replacement is often more practical where internal components have failed.
Can I replace the mechanism?
Yes, in many cases a complete multipoint mechanism can be replaced. The replacement must be compatible with the door and existing hardware or the door may require modification.
Is my door dangerous if it won't lock?
A door that cannot be securely locked is a security concern and should be dealt with promptly. A severely damaged or jammed door can also create an access or escape issue.
Why does my door work better in summer?
Thermal expansion can change the relationship between the door, frame, seals and locking points.
Why does my door only lock when open?
This commonly points towards an alignment or keep problem because the locking points aren't having to engage the frame when the door is open.
Do I need a new door?
Usually not simply because the locking mechanism has failed.
Many problems can be repaired by replacing or adjusting individual components.
Can alignment cause gearbox failure?
Yes.
Excessive resistance between locking points and keeps can increase the load transmitted through the handle and gearbox.
Why does my new gearbox keep failing?
If a replacement gearbox fails prematurely, the underlying cause should be investigated.
Possible contributing factors include:
- Poor alignment
- Excessive compression
- Damaged locking points
- Incorrect components
- Excessive mechanical resistance
- Incorrect installation
Simply fitting another gearbox may not solve the problem.
Can new handles fix a drooping handle?
They can if the handles themselves are faulty.
However, if the handle is drooping because the mechanism or spring cassette is failing, replacing the external handles alone may not solve the underlying problem.
Conclusion
Most door problems don't necessarily begin with a component suddenly breaking.
They often begin with small changes that gradually increase the load placed on the locking system.
A hinge moves slightly.
A door drops.
A keep becomes misaligned.
A locking point begins rubbing.
The handle becomes heavier.
More force is applied.
The gearbox takes the additional load.
Eventually something fails.
By the time the gearbox stops working, the original cause may no longer be obvious.
This is why accurate diagnosis matters.
A stiff key isn't automatically a bad cylinder.
A drooping handle isn't automatically a failed gearbox.
A door that won't lock isn't automatically a reason to replace the entire mechanism.
And a failed gearbox doesn't automatically mean the door itself needs replacing.
The correct repair depends on understanding the relationship between the door, frame, hinges, handles, cylinder, gearbox, mechanism, locking points and keeps.
Sometimes the solution is a simple adjustment.
Sometimes it is a new handle, cylinder or gearbox.
Sometimes the complete mechanism needs replacing.
And occasionally the door itself has reached the point where replacement is the sensible option.
The objective should always be the same:
Find the cause, repair the fault and make the complete door operate correctly — rather than simply replacing the first component that appears to be broken.
