UPVC Door Won't Lock? 9 Fixes From a Working Locksmith

A UPVC door that won't lock is one of the three most common locksmith call-outs we attend across West London and the Thames Valley. The good news: in about 60% of cases the homeowner can diagnose and even fix the problem before calling anyone out. Here are the nine causes we see in the field, ranked by how often they actually show up.

1. The door has dropped on its hinges. This is the single most common cause. UPVC and composite doors are heavy (often 35–50kg) and the flag hinges that carry them wear over time. A dropped door drags on the keeps, the multipoint hooks no longer line up with their housings, and the handle stiffens or fails to lift fully. Test: open the door, look at the gap between the bottom of the door and the threshold across the full width. If it's tighter on the handle side, the door has dropped. Fix: hinge adjustment — most flag hinges have an Allen key adjuster on the side.

2. A failed multipoint gearbox. The gearbox is the metal bar inside the door edge. When it fails, the handle either spins freely, won't lift, or won't unlock once locked. Test: try locking the door open (door swung outward so the hooks aren't engaging anything). If the handle still won't lift, the gearbox itself is the fault, not alignment. Fix: gearbox replacement — Yale Doormaster, GU Secury, ERA Vectis and Fuhr Multisafe are the four most common types.

3. The keeps are out of alignment. The keeps are the metal plates on the frame that the hooks lock into. If they're not aligned with the hooks (usually because the door has shifted or the frame has moved), the handle won't lift all the way. Fix: keep adjustment — loosen the screws, shift the keep 1–2mm in the right direction, re-test.

4. A snapped cylinder cam. After an attempted break-in, the euro cylinder may be partially snapped — the key turns but the cam inside no longer engages the gearbox. Test: insert key, turn — if it spins freely or feels slack, the cam is gone. Fix: cylinder replacement, and an immediate upgrade to TS007 3-star if it isn't already.

5. Swollen door in summer. Composite and UPVC doors expand in heat. If the door only sticks in summer, expansion is your culprit. Fix: temporary — leave the door open 20 minutes in shade. Permanent — keep adjustment, or hinge adjustment to lift the door 1–2mm.

6. Worn handle springs. The internal springs in the handle weaken over time, so the handle no longer returns to horizontal properly. Test: lift the handle — if it stays half-lifted when you let go, the spring is gone.

7. Debris in the keeps or hooks. Sounds trivial, fixes more doors than you'd think. Leaves, paint flakes or grit in the keep housing can stop the hook seating fully. Fix: vacuum out, lubricate with PTFE (NOT WD-40 — it gums up over time).

8. Bent hooks or shootbolts. After a slamming incident or an attempted forced entry, the steel hooks themselves can deform slightly. They still operate but won't engage cleanly. Fix: hook replacement, often part of a gearbox kit.

9. The wrong cylinder length. If a cylinder was replaced incorrectly with one that's too long or too short, the cam can't drive the gearbox properly. Fix: re-measure and re-fit correct length (cylinders are sized in 5mm increments — 35/35, 40/40, 45/45 etc.).

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