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Guides / uPVC Door Will Not Lock
Why a uPVC Door Will Not Lock Properly
A uPVC door that will not lock has usually failed in one of four places, and the handle tells you which. A handle that lifts but will not turn the key means the gearbox has gone, a handle that will not lift at all means the door is out of alignment, a key that spins freely means the cylinder cam has failed, and a door that locks only when pulled hard means the keeps need resetting. Three of the four are a part swap rather than a new door.
Written by Sam Gregory, locksmith in Sheffield. Updated October 2026.
What the Handle Is Telling You
Before anything else, lift the handle with the door standing open. That single test separates a mechanism fault from an alignment fault and it takes two seconds.
- The handle lifts freely with the door open but will not lift when the door is shut, which means the door is out of alignment and the hooks are catching on the keeps.
- The handle is stiff or jams with the door open, which means the mechanism itself is failing and the alignment is not the problem.
- The handle lifts but the key will not turn afterwards, which is the gearbox, and it is the most common failure of the four.
- The handle lifts and the key turns but nothing locks, which means the cam inside the cylinder has sheared.
Doing that test before you ring saves a visit and usually saves money, because the repair for an alignment fault and the repair for a failed gearbox are not the same job or the same price.
What a Multipoint Mechanism Actually Is
A multipoint mechanism is the long metal strip running down the edge of the door, carrying hooks, rollers and a central gearbox. Lifting the handle drives the hooks out into the frame and turning the key locks them there.
The gearbox in the middle is the part that does the work and the part that wears out. It is a mechanical component operating several times a day for years, and it fails long before the door, the frame or the glass does.
That is the whole reason a uPVC door can be twenty years old and still perfectly sound while refusing to lock. The door has not failed. One component inside it has, and it is replaceable.
The Four Faults and What Each One Needs
Four faults account for almost every uPVC door that stops locking. The table names what you notice, what has actually failed and what the repair involves.
| What you notice | What has failed | What the repair involves |
|---|---|---|
| Handle lifts, key will not turn | The gearbox inside the mechanism | Replace the gearbox, or the mechanism if the strip is worn |
| Handle will not lift when shut | Door alignment, not the lock | Adjust the hinges and reset the keeps |
| Key spins with no resistance | The cam on the euro cylinder | Replace the cylinder, keep the mechanism |
| Door locks only when pulled hard | Keeps out of position, seals compressed | Reset the keeps and adjust the compression |
Only the first of those four is likely to need a sizeable part, and even then a failed gearbox can often be replaced on its own rather than swapping the whole strip. What that costs and why is set out on the what decides a locksmith price page.
The Warning Signs That Come First
A uPVC door rarely fails without warning. It gives you weeks of signals and most people read them as the door being awkward rather than the lock being on its way out.
- The handle needs lifting harder than it used to, and you have started leaning on the door to do it.
- The key needs a slight jiggle or a particular angle before it turns.
- The door has to be pulled towards you before the handle will lift at all.
- You hear a grinding or clicking inside the door when the handle goes up.
- The handle has gone floppy, or it lifts without the usual resistance.
The fifth one is the last warning. A handle that has lost its resistance means the gearbox is close to giving up, and when it goes it almost always goes with the door shut. That is the difference between a booked appointment and an emergency call out, and it is usually only a few days apart.
Why Doors Drop Out of Alignment
A uPVC door is hung on adjustable hinges and the frame moves with the weather, so alignment drifts over time rather than failing suddenly.
Heat expands the slab, cold contracts it, and a door that locks perfectly in March can start catching in July. The hooks need to meet the keeps within a few millimetres, so a small amount of drop is enough to stop the handle lifting when the door is shut.
The fix is adjustment rather than parts. Hinges on a uPVC door adjust in three directions, and resetting them is usually a twenty minute job that costs less than any part. A locksmith who quotes you for a mechanism when the handle lifts freely with the door open has not done the handle test.
Can You Fix a uPVC Door Yourself
Some of it, and the honest split is worth knowing before you order a part.
- A cylinder change is the one most people can do, because it is one screw through the edge of the door, as long as the replacement is measured correctly.
- Hinge adjustment is possible with the right allen key, though it is easy to make a binding door worse by adjusting the wrong axis.
- A gearbox or full mechanism replacement is not a sensible job to attempt, because the mechanism has to be identified by its exact dimensions and backset, and an incorrect part will not fit the door at all.
The measuring is what catches people out on all three. A euro cylinder measured wrong either stands proud of the handle, which is the single easiest thing for a burglar to attack, or sits too short and will not engage. Getting the size right matters more than getting the brand right, and the measurement runs from the centre of the fixing screw to each face of the door rather than end to end.
When a uPVC Door Does Need Replacing
Three situations genuinely call for a new door rather than a repair, and they are all about the slab or the frame rather than the lock.
- The slab itself has warped or delaminated, which no amount of adjustment will correct.
- The frame has moved or rotted at the fixings, so there is nothing solid to adjust against.
- The door was damaged in a forced entry badly enough that the edge will not hold a mechanism.
Outside those three, a uPVC door that will not lock is a repair. If somebody has quoted you for a replacement without first checking the handle with the door open, it is worth getting a second opinion before spending the money.
Describe what the handle is doing
Send a photo of the door from the outside with the lock and handle in frame, and say what happens when you lift the handle. Sam replies with which part has failed and what the repair costs. If the door is already shut and will not open, call or WhatsApp him instead.
Repairs This Guide Leads To
Each of these pages covers the repair in full, including the parts and how the job runs.
Gearboxes, multipoint mechanisms and doors that will not lock.
The same faults on a heavier door that drops more.
The same mechanism family, fitted to windows.
For when the door has already shut and will not open.
uPVC Door Lock Questions Answered in Short
Short answers on the handle that will not lift, keys that spin, doors that need a shove and whether the whole door has to go. If your question is not here, call Sam on 07842 685254.
My uPVC door handle lifts but the key will not turn
The gearbox inside the multipoint mechanism has failed. It is the most common uPVC door fault and it is a part swap rather than a new door. Ring while the door still opens, because these usually give up with the door shut.
The handle will not lift at all when the door is closed
The door is out of alignment rather than broken. The hooks are catching on the keeps before they can travel, which is why the handle lifts freely when the door is open. It is a hinge adjustment in most cases.
My key spins round and round with no resistance
The cam on the euro cylinder has sheared, so the key is turning but nothing is being driven. The cylinder is replaced and the mechanism is left alone, which is one of the cheaper repairs.
The door only locks if I pull it hard towards me
The keeps are slightly out of position or the seals have compressed, so the hooks are not meeting their housings cleanly. Resetting the keeps usually fixes it and no parts are needed.
Does a uPVC door that will not lock need replacing
Almost never. The slab, the frame and the glass outlast the mechanism by years, and in most cases one component inside the door has failed. A replacement is only justified when the slab has warped, the frame has moved or the door was damaged in a break in.
Can the gearbox be replaced on its own
Often, yes, and it costs less than replacing the whole strip. It depends on whether the mechanism is one where the gearbox comes out separately and whether the rest of the strip is still sound. Ask which one you are being quoted for.
How long does a uPVC mechanism last
Years rather than decades of hard use, and the life depends on how well the door is aligned. A door that has to be forced every time wears its mechanism out far faster than one that closes cleanly, which is why alignment is worth fixing early.
Why did it fail suddenly when it was fine yesterday
It almost certainly was not fine yesterday. A mechanism gives weeks of warning through a stiffer handle, a key that needs a jiggle and a door that needs pulling, and those get read as the door being awkward rather than the lock failing.
Is it worth lubricating the lock
Yes for the cylinder, using a graphite or PTFE based lubricant rather than oil. Oil attracts dust and gums up the pins over time. Lubrication will not revive a failed gearbox, though, and it is not a substitute for adjustment.
Can I still use the door while it is like this
Usually, but not for long, and the risk is being locked out rather than being insecure. A mechanism that is failing tends to seize with the door shut, so a door that still opens is a door worth booking in now.
Will my insurer care which lock is fitted
They care about the standard rather than the brand. uPVC and composite doors are usually asked for a cylinder rated TS007 3 star or Sold Secure Diamond. Tested products are listed by Secured by Design, and fitting one is covered on the 3 star cylinders fitted page.
Who repairs uPVC doors, a locksmith or a window company
Either can, but a locksmith is usually quicker and cheaper for a lock or mechanism fault, because it is a part they carry. A window company is the right call when the slab, the frame or the glazing is the problem rather than the lock.
How do I get this looked at
Describe what the handle does rather than what you think is wrong, and send a photo of the door from the outside. Every way of reaching Sam is on the ways to reach Sam.