uPVC door won't lock — five reasons and what to do

If you're at the door now with a handle that won't lift, a key that turns but won't lock, or a door that just won't close properly, here's the diagnostic. There are essentially five reasons a uPVC door stops locking. Most homes hit at least one in the life of the door, usually around years 8–15.

We cover the technical detail and pricing on our uPVC door repair page. This post is the diagnostic — what's actually wrong, and what each problem actually costs.

1. The gearbox has failed (most common)

The gearbox is the part of the multipoint mechanism the handle turns. When you lift the handle, the gearbox drives the long internal strip that throws all the hooks, bolts and rollers into the keeps in the frame. It's the highest-stress component in the door and the most common failure.

Symptoms:

• Handle lifts but doesn't engage the lock
• Handle is increasingly stiff to lift
• Handle lifts all the way up with no resistance and nothing happens
• Door visibly closes but key won't turn
• You hear a "clunk" inside the door but the bolts don't move

Fix: Gearbox replacement, typically £140–£280 fitted in Manchester. You don't usually need a whole new mechanism — most uPVC doors take a replaceable gearbox cassette that slots into the existing strip.

Timing: Gearboxes generally last 8–12 years of domestic use, faster on heavily used doors (rented properties, families with kids, busy back doors).

2. The door has dropped on its hinges

uPVC doors are heavy — typically 30–60kg with the glass. Over years of opening and closing, the hinges (especially on doors with three hinges, where the centre one carries the most load) shift slightly. When the door drops 2–3mm, the hooks and bolts inside the mechanism stop lining up with the keeps in the frame, and the lock won't engage.

Symptoms:

• Door scrapes the threshold at the bottom corner when opening
• You have to lift the door slightly to get the handle to engage
• Lock used to work fine and gradually got worse
• Door catches the frame at one corner
• More pronounced in summer (warm expansion) or after a heavy slam

Fix: Alignment and hinge adjustment, typically £80–£140. The cheapest fix on the list — and it prevents the gearbox dying early, which is what happens when you force a misaligned mechanism for months.

Worth doing before the gearbox goes. A small adjustment now saves the bigger bill later.

3. Cold snap stiffness

uPVC contracts in the cold. Manchester winters aren't extreme, but a week of sub-zero nights tightens the door enough that a marginal mechanism — already on the edge — fully stops working.

Symptoms:

• Door works fine in summer
• Stops working below about 5°C
• Comes back when it warms up
• Often combined with one of the other issues — a worn gearbox plus cold tightening, or a slightly dropped door plus cold stiffening

Fix: Usually it's a combination job. We diagnose what else is going on, fix the underlying issue (gearbox or alignment), and the cold-weather problem goes away with it.

If it's purely cold-weather and nothing else is wrong, the door is on the brink of needing one of the bigger fixes. Worth doing now rather than waiting for the gearbox to go in February.

4. Handle wear or spindle damage

The square metal spindle that connects the inside handle to the outside handle (and to the gearbox in the middle) can wear, twist or shear. Cheap handles fitted with cheap spindles are especially prone to this — the spindle rounds off over time and the handle starts to slip on the spindle without actually turning the gearbox.

Symptoms:

• Handle feels loose or wiggles independently of the door
• Handle goes through full rotation but nothing happens inside the door
• Handle is suddenly very easy to lift but doesn't engage anything
• Inside handle works but outside handle doesn't, or vice versa

Fix: Handle replacement (both sides) with a new spindle, typically £70–£140 fitted. We use solid steel spindles and quality handles. The bargain-basement handles fail again within a couple of years; the proper ones last the life of the door.

5. Cylinder fault

The cylinder is the small barrel where the key goes. It controls the dead-lock action — the key turning the cam that locks the mechanism into place after the handle has lifted. If the cylinder fails, the handle still lifts and lowers, but the key won't turn or the lock won't dead-lock.

Symptoms:

• Handle works fine, key won't turn at all
• Key turns part-way and sticks
• Key turns freely with no engagement
• Cylinder feels rough or gritty when you try the key
• Locks fine but you can't unlock from outside

Fix: Cylinder replacement, typically £80–£180 for standard, £140–£250 for a 3-star anti-snap upgrade. If you're already replacing, this is the right moment to upgrade to anti-snap — see are anti-snap locks worth the extra cost?.

What not to do

The single biggest mistake we see: forcing a uPVC door that's started to fail. The mechanism is full of small steel components running in a long strip; forcing the handle when something is binding bends a component, and now you need a full mechanism replacement (£180–£380) instead of a gearbox swap (£140–£280).

If the door has started to stick, stop using force, and book a repair before it gets worse. The mechanism is almost always saveable if we get to it before it's been forced for weeks.

Quick self-diagnosis

A two-minute test you can do now:

1. Open the door fully. Lift the handle with the door open and the mechanism free. Does it lift easily? If yes, the problem is alignment, not the gearbox. If no, gearbox.
2. Look at the keeps (the metal slots in the frame where the hooks engage). Are they scratched or marked from the hooks hitting them out of line? Alignment.
3. Stand outside, close the door, lift the handle. Does it feel tight? If yes, even with the mechanism freshly tested in step 1, it's keep/door alignment.

If all three suggest alignment, you might be 80 quid away from a working door. If the handle is stiff even with the door open, it's likely the gearbox.

Where you fit in Manchester

The pattern in different bits of the city:

• Older estates in Salford and Old Trafford — 1990s and 2000s doors at the gearbox-end-of-life age. Lots of gearbox swaps.
• Newer composite doors in Didsbury and Chorlton — usually alignment work, sometimes early-failure gearboxes on heavy-use back doors.
• High-density rental in Withington — accelerated wear from rotating tenants and forced doors. Higher rate of full mechanism replacements.

When to call us

Call us when the handle is stiffening, when the key won't turn first time, when the door is dragging on the threshold, or when something has just stopped working. Don't force it in the meantime. We cover Manchester every day and carry the common gearboxes and mechanisms on the van — most jobs finish on the first visit.