UPVC Door Won't Lock? 5 Causes & Fixes

1. Failed multipoint gearbox (most common)

The gearbox is the heart of the multipoint mechanism — the box the handle spindle passes through. When its internal springs break, the handle drops instead of springing back, and the hooks and rollers won't throw. This is our single most common UPVC call.

Fix: gearbox replacement, from £95 including parts. We carry ERA, Fullex, Avocet, Mila and Fuhr gearboxes and match the exact model — a wrong gearbox is a common cause of repeat failure.

2. Dropped door

UPVC doors are heavy and hinges wear. When the door drops even a few millimetres, the locking points no longer align with their keeps — you end up lifting or slamming the door to lock it, which strains the gearbox and accelerates cause #1.

Fix: hinge adjustment and realignment, from £65. Often combined with a gearbox service if the mechanism has been strained.

3. Misaligned keep or strike plate

The keeps — the plates on the frame the bolts engage — shift with seasonal movement and general wear. Symptoms: the key turns but the door doesn't feel secure, or you have to push the door hard while turning.

Fix: keep adjustment and repositioning. A quick job on its own, often done as part of a service visit.

4. Seized or broken locking point

The individual hooks, rollers or deadbolts along the door edge can seize from lack of lubrication or break under strain. You'll feel grinding, or one section of the door won't engage while the rest does.

Fix: individual locking point replacement or full strip replacement if the gearbox failure has damaged the strip.

5. Worn or wrong-sized cylinder

Sometimes the mechanism is fine and the cylinder is the problem — worn pins making the key stiff, or a replacement cylinder fitted too long, fouling the mechanism. A cylinder protruding beyond the handle is also a snapping risk.

Fix: correctly sized replacement cylinder, from £55 — ideally a TS007 3-star anti-snap while the door is being serviced.

What not to do

Don't force the handle — forcing a failing gearbox is how spindles snap and strips crack, turning a £95 repair into a £300+ one. And don't spray oil-based lubricants into the mechanism; they attract grit. A silicone-based lubricant on the locking points, used sparingly, is fine as maintenance — but if the door already won't lock, it needs diagnosis, not lubricant.

Questions about this topic

Can you fix a UPVC door that won't lock today? +

In most cases, yes — same-day across Dulwich and South London. We carry the common gearboxes and mechanisms, so most faults are fixed in a single visit. Call 07984 547185.

Is it cheaper to repair or replace the whole mechanism? +

Repair of the failed component is almost always cheaper. A gearbox replacement starts from £95 including parts; a full strip is only needed when the strip itself is damaged. We diagnose first and quote the actual fault — never a blanket mechanism swap.