Why Won't My uPVC Door Lock? Alignment, Hinge and Gearbox Diagnosis

Summary

"The front door won't lock" is a daily call for locksmiths, window fitters and general maintenance tradespeople, and the fault is frequently misdiagnosed as a broken lock when the lock is fine and the door has simply moved. uPVC doors are heavy, hung on adjustable hinges in a frame that moves with the seasons, and locked by a multipoint mechanism whose hooks, rollers and bolts have to land in keeps on the frame within a couple of millimetres. A door that has dropped 3 mm on its hinges presents its hooks to the wrong place, the handle will not lift, and the customer either forces it (and breaks the gearbox) or assumes the lock is broken (and pays for one they do not need).

The diagnostic logic is to separate alignment from mechanism from cylinder. Alignment faults show up as a handle that works perfectly with the door open and badly with it closed. Mechanism faults show up with the door open. Cylinder faults show up as a key problem with a handle that is working. Once you know which of the three you are dealing with, the repair is predictable and quick, and you can price it over the phone with reasonable confidence.

This guide covers the diagnosis, the hinge and keep adjustments, how to identify and replace a failed gearbox, cylinder replacement and the security standards that apply, and what to charge. For the replacement procedure in full see upvc door lock mechanism replacement; for cylinder and hardware standards see security locks and security hardware.

Key Facts

• Three fault families — alignment (door or frame moved), mechanism (multipoint gearbox or strip failed), cylinder (key will not turn or operate the cam)
• The open-door test — operate the handle and key with the door open. Works perfectly open but not closed: alignment. Stiff or dead open: mechanism. Handle fine, key fails: cylinder
• Multipoint lock anatomy — a central gearbox behind the handle drives a long faceplate strip carrying hooks, deadbolts, rollers or mushroom cams at two to five points; the handle lifts to throw them into keeps on the frame and the key deadlocks them
• Gearbox failure signs — handle floppy or will not lift with the door open; handle lifts but nothing moves on the strip; a grinding or click then nothing; handle only works at a particular angle; key turns freely without locking
• Dropped door signs — hooks or bolts scoring the keeps; a visible gap wider at the top of the lock side than the bottom; the door catches on the sill or the frame at the top corner on the latch side; handle lifts only when the door is lifted or pushed
• Hinge types — flag hinges (most common, three adjustments: height, lateral, compression), butt hinges (height and lateral via cams or packers) and rebate hinges; adjustment is usually with a 4–5 mm Allen key or a Torx T15–T30
• Adjustment range — typically ±2 mm height, ±2–3 mm lateral and ±1–2 mm compression per hinge; beyond that the frame or the sash has moved and the fix is re-packing or re-fixing the frame, or re-toeing and heeling the glazed sash
• Keeps — the frame-side plates the hooks and bolts enter; most are adjustable laterally by 1–2 mm with a screwdriver or Allen key and can be moved up and down by refixing
• Cylinder standards — euro profile cylinders to BS EN 1303; anti-snap, anti-bump and anti-drill cylinders to TS 007 3-star (BSI Kitemark) or Sold Secure SS312 Diamond; Approved Document Q (new dwellings) and PAS 24 expect this level
• Cylinder sizing — measure from the centre of the cam screw hole to each end (e.g. 35/45 mm); the cylinder should not protrude more than 3 mm beyond the handle backplate
• Lubrication — a light silicone or PTFE spray on the strip, hooks and keeps once a year; never grease into the gearbox and never WD-40 into the cylinder, which gums the pins; use a graphite or dry PTFE cylinder lubricant
• Pricing (2026) — adjustment visit £60–£110; gearbox replacement £100–£250 fitted (gearbox £35–£90); full multipoint strip £180–£350 fitted; anti-snap cylinder £60–£130 fitted; handle set £40–£90 fitted; emergency entry to a jammed door £90–£180 (see locksmith lock change pricing guide)

Quick Reference Table

Detailed Guidance

Step 1 — the open-door test

Open the door fully. Lift the handle: the hooks, bolts and rollers should move smoothly out of the faceplate and the handle should return to horizontal on its own. Turn the key both ways: it should throw the deadbolt and lock the handle. Then close the door and repeat.

• Everything works open, something fails closed — alignment. Go to Step 2.
• Handle is stiff, dead or floppy with the door open — mechanism. Go to Step 4.
• Handle fine, key fails open or closed — cylinder. Go to Step 5.

If the door is currently stuck shut and the handle will not move, do not keep trying. Lift the door by its handle while someone else pushes or pulls at the lock edge, and try the handle under that load; if it releases, the fault is alignment and you have avoided breaking the gearbox. If it will not release, see the section on gaining entry.

Step 2 — reading the alignment

With the door closed and unlocked, look at the gap between sash and frame all the way round. It should be even, typically 4–6 mm. A gap that is wider at the top of the lock side than the bottom, or a door that rubs on the sill at the lock side, means the door has dropped on its hinges. Open the door and look at the keeps: bright metal scoring on their top or bottom edges shows where the hooks have been landing.

Check the hinges themselves. Grasp the door at the lock edge and lift: play or movement at the hinges means loose hinge screws, often because the screws are into the plastic rather than the steel reinforcement in the sash. Re-fix with longer screws into the reinforcement before any adjustment; adjusting a hinge that is loose achieves nothing.

Step 3 — hinge and keep adjustment

Most uPVC doors made since the late 1990s hang on flag hinges, which have:

• Height adjustment — usually an Allen screw in the bottom of the hinge body or under a cap on top; a quarter turn moves the door about 0.5 mm. Raise a dropped door in small increments on all hinges equally, then check the gap and the handle
• Lateral adjustment — a screw on the face of the hinge that moves the sash towards or away from the hinge side; use it to centre the door in the frame so the lock-side gap is even
• Compression — an eccentric cam or screw on the hinge that pulls the sash tighter onto the weather seal; too much makes the handle stiff, too little makes the door rattle when locked

Older butt hinges and some budget flag hinges have fewer adjustments; where height is the problem on a non-adjustable hinge, a 1–2 mm nylon packer under the hinge leaf on the frame side is the accepted fix.

Work in this order: tighten fixings, set height so the door clears the sill and the gap is even top to bottom, set lateral so the lock-side gap is even, then set compression so the handle lifts with light resistance and the door does not rattle. Lubricate the strip and keeps. Close and test. Only then adjust keeps: most have an eccentric adjuster or a sliding plate allowing 1–2 mm of lateral movement to meet a hook that is close but not quite entering. If the hooks are more than about 3 mm off the keeps after the hinges are at the end of their travel, the frame has moved or the sash is out of square and you are into re-fixing the frame or toe-and-heeling the glazing, which is a window fitter's job and priced accordingly.

Step 4 — identifying and replacing the gearbox

With the door open, a handle that is floppy, will not lift, or lifts without moving the hooks means the gearbox has failed. The usual failure is the cast follower (the square that the handle spindle passes through) cracking, or the internal spring breaking, often as a result of years of forcing a misaligned door.

Replacing it: remove the handles (two through-bolts), remove the cylinder (one retaining screw in the faceplate at cylinder height, key turned slightly to align the cam), remove the faceplate screws along the lock edge and withdraw the strip far enough to free the gearbox. Most gearboxes are removable from the strip with two screws; on some older mechanisms the whole strip is one piece and must be replaced complete.

Identification is the hard part. Note the brand stamped on the faceplate or gearbox (common UK brands include Yale, ERA, Fullex, GU, Winkhaus, Maco, Avocet, Mila, Roto, Lockmaster, KFV and Fuhr), and measure the backset (centre of spindle to faceplate face, typically 28, 30, 35 or 45 mm), the PZ (centre of spindle to centre of cylinder, typically 92 mm, with 72 and 70 mm on some), the faceplate width (16 or 20 mm), the spindle size (8 mm) and whether the gearbox is a single-spindle, split-spindle or lift-lever type. Photograph the gearbox and the faceplate ends. A generic replacement gearbox matched on backset, PZ and spindle type fits the large majority of doors; obsolete strips may need a full-strip conversion kit. Fit, test with the door open, then closed, and lubricate.

Price it as a fixed job: gearbox £35–£90, 45–90 minutes of labour including identification, £100–£250 fitted. Where the whole strip is replaced, £180–£350.

Step 5 — cylinder faults

If the handle works and the key does not, remove the cylinder (retaining screw out, key turned to align the cam, pull from the keyed side). Try the key in the cylinder out of the door: if it still will not turn, the cylinder has failed internally or the key is worn; if it turns freely out of the door, the problem is the cam not engaging the gearbox, which is a gearbox fault or a cylinder with the wrong cam type.

Replace like for like in length (measure centre-of-cam-hole to each end) but upgrade the security. The security standards are:

• BS EN 1303 — the basic performance standard for cylinders
• TS 007 — the UK Kitemarked standard for cylinders and handles rated 1-star to 3-star against snapping, bumping, drilling and picking; a 3-star cylinder alone, or a 1-star cylinder with a 2-star security handle, achieves the 3-star total
• Sold Secure SS312 Diamond — the alternative anti-snap benchmark recognised by insurers and Secured by Design

Approved Document Q (England) requires doors to new dwellings to meet PAS 24, which in practice means a 3-star or Diamond cylinder arrangement. On an existing house there is no legal requirement, but a customer with a 1990s cylinder protruding 10 mm beyond the handle has the single most exploited weakness in UK domestic burglary, and the upgrade is a £60–£130 job. Lubricate cylinders with a dry PTFE or graphite product only.

Gaining entry to a jammed door

If the door is locked and the handle will not move, the gearbox has usually failed in the locked position. Non-destructive options first: lift the door hard at the lock edge while working the handle; try the handle from the other side if accessible; remove the handle and try turning the spindle directly with a screwdriver blade. If the cylinder still works, the deadbolt can be withdrawn with the key but the hooks stay thrown; on many gearboxes, with the handles off and the cylinder out, the follower can be turned with a square-section tool to retract the hooks. Failing that, the cylinder is snapped and the gearbox manipulated through the cylinder aperture, which is a locksmith's technique and damages nothing but the cylinder you were replacing anyway. Drilling or prising the faceplate is the last resort and costs a full strip.

Seasonal movement

A door that locks in summer and jams in winter, or the reverse, is moving with temperature. Dark uPVC on a south or west elevation expands enough in sun to foul the frame; composite doors and large sashes are worse. Set the adjustment at a mid-season position and tell the customer a small seasonal tweak may be needed; where the problem is severe, lateral and compression adjustment at the mid-point, plus checking that the sash is properly toed and heeled so it is not racking, is the most that can be done short of a replacement door.

Frequently Asked Questions

Why does the handle work when the door is open but not when it is shut?

Because the lock is fine and the door has moved. The hooks and bolts travel freely in open air but hit the edges of their keeps when the door is closed, because the sash has dropped or shifted a few millimetres on its hinges. Adjust the hinges to centre the door in the frame and the handle will lift normally. Forcing it in this state is how gearboxes get broken.

How much should a gearbox replacement cost?

£100–£250 fitted in 2026 for a standard single-spindle gearbox matched on backset and PZ, including identification, removal, fitting, adjustment and lubrication. Obsolete or unusual mechanisms that need the whole strip replaced run £180–£350. Emergency out-of-hours entry adds £50–£100. Beware of quotes well below this that then substitute a full-strip change on site.

Is it worth upgrading the cylinder while I am there?

Yes. If the existing cylinder is not a TS 007 3-star or SS312 Diamond anti-snap type, or it protrudes more than 3 mm beyond the handle, it is the weak point of the door. The upgrade is £60–£130 fitted, takes ten minutes while the handles are off, and is the single most effective domestic security improvement available. Most customers accept it when it is explained.

Do I need a locksmith or a window fitter?

For alignment and gearbox work either will do; window fitters are generally better at hinge, frame and toe-and-heel problems, locksmiths at cylinders, entry and obsolete mechanism identification. A general maintenance tradesperson with the right Allen keys, a selection of generic gearboxes and a cylinder stock can handle 80% of calls. The jobs to pass on are a frame that has moved in the wall and a sash that is out of square.

Can WD-40 be used on a stiff uPVC door lock?

On the strip, hooks and keeps a light spray is harmless but a silicone or PTFE lubricant lasts longer. Never spray oil-based products into the cylinder; they attract dust and gum the pins so the key sticks. Use a dry graphite or PTFE cylinder lubricant. A handle that is stiff because of alignment will not be cured by any lubricant.

Regulations & Standards

• Building Regulations 2010, Approved Document Q (England) — security in new dwellings: doors to meet PAS 24, including cylinder protection

• PAS 24:2022 — enhanced security performance requirements for doorsets and windows (the test standard behind Approved Document Q and Secured by Design)

• BS EN 1303:2015 — building hardware: cylinders for locks, requirements and test methods

• TS 007:2014 — Kitemark technical specification for enhanced security performance of replacement cylinders and protective hardware (1-star to 3-star rating)

• Sold Secure SS312 Diamond — independent anti-snap cylinder standard recognised by insurers and Secured by Design

• BS EN 12209 — mechanically operated locks and locking plates (multipoint lock cases)

• BS EN 1935 — single-axis hinges (the performance standard adjustable door hinges are tested against)

• BS 8213-4:2016 — code of practice for the survey and installation of windows and external doorsets (installation and adjustment of replacement doors)

• BS 3621 — thief-resistant lock assemblies (mortice locks on timber doors; not applicable to euro cylinders but often cited by insurers alongside TS 007)

• GOV.UK — Approved Document Q: Security in dwellings — requirements for doors in new dwellings

• Secured by Design — Doors and cylinders — police-preferred specification and TS 007 / SS312 guidance

• Master Locksmiths Association — Consumer advice — cylinder snapping and multipoint lock guidance

• Sold Secure — SS312 Diamond cylinders — the Diamond anti-snap standard

• BSI Kitemark — TS 007 cylinders — Kitemark scheme for cylinders and security hardware

• Door and Hardware Federation (DHF) — industry guidance on doorset hardware and adjustment

• upvc door lock mechanism replacement — the full gearbox and strip replacement procedure

• security locks — cylinder and lock standards explained

• security hardware — handles, hinges and keeps that meet PAS 24

• door not closing properly — doors that bind, catch or spring open

• composite vs upvc door — how door construction affects alignment and movement

• part q security — Approved Document Q in full

• locksmith lock change pricing guide — pricing lock, cylinder and entry work

• upvc window hinge and handle replacement — the window equivalent of these faults