The handle won't lift. The handle lifts but the key won't turn. The lock engages with the door open but not closed. Or you can lock from inside but not from outside. uPVC and composite doors fail in remarkably consistent ways, and the cause is almost always one of four problems: a dropped door, a failed gearbox, a seized cylinder, or expansion from heat. This guide walks through diagnosis, DIY fixes that genuinely work, and when to stop and call a locksmith.
- Locks fine when open, jams when closed? → Dropped door. Allen-key hinge adjustment fixes it.
- Handle won't lift at all? → Failed gearbox. Locksmith job, £150-£300.
- Handle lifts but key won't turn? → Seized cylinder. Lubricate or replace.
- Worse in hot weather only? → Door expansion. Hinge adjustment.
The four causes (in order of likelihood)
1. Dropped door (60% of cases)
uPVC and composite doors hang on three hinges, and over 5-10 years the hinges sag — especially on heavy doors or south-facing sun-baked ones common in Cornwall. The door drops a millimetre or two, and the multipoint bolts no longer align with their strikes (the slots in the frame). Lock engages with the door open but jams when you try to lock it closed.
Fix: Most uPVC hinges have an Allen key adjustment (3, 4 or 5 mm hex socket on the hinge body). Insert the Allen key, turn 1/4 turn at a time, test closing. Top hinge lift = raises the latch side. Bottom hinge lateral = pulls the latch side towards the frame. Takes 5 minutes. There are good YouTube videos for each hinge brand (Mila, ERA, Roto, Maco).
2. Failed multipoint gearbox (20%)
The gearbox is the metal mechanism inside the door that translates handle/key motion into the locking bolts firing. After 7-15 years of use, the internal cogs wear or the springs fatigue. Symptom: handle won't lift at all, or lifts halfway and stops, or the key turns but the latch doesn't retract.
Fix: Gearbox replacement. £150-£300 in Cornwall including the part. The job takes 30-90 minutes and the locksmith needs to bring or order the matching gearbox (there are dozens of types: ERA Fullex, Yale, Avocet, Roto, etc.). Photograph the existing gearbox before calling so you can describe it.
3. Seized cylinder (15%)
The euro cylinder (the brass cylinder you put the key in) seizes when dirt, salt, or old lubricant gums up the pin chambers. Salt air on Cornwall coastal homes accelerates this. Symptom: handle lifts fine, but the key won't turn — or only turns partway.
Fix: Graphite or PTFE spray first (puff into the keyway, work the key in/out 5-10 times). If that doesn't free it, the cylinder needs replacing — £80-£140 fitted for a standard cylinder or £100-£180 for a TS007 3-star anti-snap upgrade (worth doing if your cylinder is old enough to need replacing anyway — see our anti-snap upgrade guide).
4. Heat expansion / cold contraction (5%)
uPVC expands in heat. On a 28°C July afternoon (rare but happens in Cornwall), a slightly-dropped door becomes a fully-jammed door. The same door is fine in November. Sometimes it's the opposite: cold contracts the frame in winter and a previously OK door starts catching.
Fix: Hinge adjustment as for cause #1 — but you may need to set it as a compromise between summer and winter positions. Some installers recommend a small adjustment in spring and another in autumn for badly-fitted doors.
The DIY fix checklist
- Try locking with the door open. If the handle lifts and locks fine with the door open, the lock mechanism is OK — your problem is alignment. Skip to step 3.
- Try locking with the door fully closed but unlatched. If lifting the handle while pulling/pushing the door slightly helps, alignment is the cause.
- Find the hinge adjustment screws. Open the door. Look at the hinges from the inside. Modern uPVC hinges have small caps or covers — pop them off to reveal Allen-key sockets.
- Adjust 1/4 turn at a time. Top hinge lift compensates a dropped latch side. Test by closing and locking after each adjustment.
- Lubricate the cylinder and gearbox. Graphite spray in the keyway; silicone or PTFE on the bolts and latch.
- If handle still won't lift, stop. Forcing a stuck handle will shear the gearbox cogs and turn a £150 gearbox swap into a £300+ job.
What never to use
- WD-40 in the cylinder. Short-term lubricant, long-term gummy residue. Use graphite, PTFE, or proper silicone lock spray.
- Excessive force on a stuck handle. The internal cogs are brass or zinc-alloy and will shear. Once sheared, the whole gearbox needs replacing.
- Hammering the cylinder. Cracks the housing, deforms the cam, and may damage the door faceplate.
- Drilling. Last-resort even for locksmiths. If you drill the wrong spot, you damage the multipoint mechanism behind the cylinder.
What it costs in Cornwall
| Job | Typical cost |
|---|---|
| Hinge adjustment (locksmith visit) | £60 – £90 |
| Cylinder replacement (standard) | £80 – £140 |
| Cylinder upgrade (TS007 3-star anti-snap) | £100 – £180 |
| Gearbox replacement | £150 – £300 |
| Full multipoint mechanism replacement | £200 – £400 |
| Handle set replacement | £60 – £140 |
When the door has dropped beyond hinge adjustment
If maxing out the hinge adjustment still doesn't align the door (common on 20+ year old doors), the door itself has sagged from the corner-welds opening up. At that point, you're looking at either:
- Door slab replacement: £400-£800 for the door alone; £700-£1,400 fitted (a glazier/installer job, not strictly a locksmith)
- Full door + frame replacement: £1,200-£2,500 fitted
Worth getting two quotes if you're at this stage.
Got a uPVC door that won't lock? Submit your postcode and we'll match you with a Cornwall locksmith who'll diagnose on arrival and only swap what actually needs swapping.
Frequently asked questions
Why does my uPVC door only lock when it's open?
The lock mechanism is fine — your door has dropped on its hinges so the multipoint bolts don't align with their strikes in the frame. Allen-key hinge adjustment usually fixes it in 5 minutes. If you've maxed the hinges and it still won't align, the door itself has sagged.
Why won't my uPVC door handle lift to lock?
Most commonly the multipoint gearbox has failed — internal cogs or springs have worn out after 7-15 years. Gearbox replacement in Cornwall: £150-£300 including the part. Don't force the handle — you'll shear remaining cogs and make it worse.
Can I fix a dropped uPVC door myself?
Yes — most uPVC hinges have an Allen-key (3, 4, or 5 mm) adjustment for height and lateral position. Pop off the hinge caps, insert the Allen key, turn 1/4 turn at a time, test by closing and locking. Takes 5-10 minutes once you know what you're looking at.
My uPVC door is only stiff in hot weather — what gives?
uPVC expands in heat. A door that's marginally dropped becomes a fully-jammed door on a 28°C day. Allen-key hinge adjustment will fix it — set it as a compromise that works in both seasons. Cornwall has milder summers than inland UK, but south-facing doors still see this in July-August.
Should I just replace the whole door?
Only if the door slab itself has sagged (rare on doors under 15 years old). Most "broken" uPVC doors are gearbox + hinge + cylinder issues totalling £150-£400 to repair — vs £700-£2,500 to replace.