Most uPVC doors that will not lock have one of three faults: the door has dropped and its locking points miss the frame, the gearbox inside the door is failing, or the cylinder is worn or the wrong length. A simple test tells you which. Open the door and try the handle gently. If it works smoothly open but not closed, the likely cause is alignment. If it is still stiff, floppy or jammed with the door open, the fault is inside the mechanism. In both cases, do not force it.
How the lock works
A uPVC door has a multipoint lock. A gearbox sits inside the door behind the handle. When you lift the handle, the gearbox drives hooks, rollers or bolts along the edge of the door into keeps (metal plates) in the frame. Turning the key then locks it in that position. Because everything runs through the gearbox, a fault in one part can look like a fault in another.
Three common faults
1. The handle will not lift to lock, or only lifts if you pull the door in. If the handle lifts normally with the door open but not when it is closed, the locking points are usually binding against the keeps. Locksmiths describe this as the door having dropped on its hinges. Signs include the door catching on the frame, uneven gaps around the edge, and having to lift the door to close it.
2. The key turns but nothing happens. A published locksmith guide says that if the key turns with no resistance and the lock does not operate, the cylinder cam may be broken or the cylinder may be too short to reach the gearbox. If the key turns with resistance and nothing happens, the gearbox is not responding. This is one reason an experienced locksmith checks both before replacing either.
3. The handle drops, is floppy or spins without locking anything. A handle that does not spring back, or spins freely without operating the lock, usually points to a worn spring, spindle or gearbox. One locksmith's guide notes that loose handle screws can cause some movement, but that tightening them will not fix every loose handle.
What you can safely check
Do these in order. Stop at any step that needs force.
- Test with the door open. Lift and lower the handle gently, then try the key. Compare how it feels open and closed.
- Look for rubbing. Check the keeps in the frame and the edge of the door for scrape marks where hooks or rollers are catching.
- Check the gaps. Uneven gaps around the door, or a door that needs lifting to close, suggest it has dropped.
- Check the handle screws you can see are not loose.
- Stop if it is stiff with the door open. A stiff or crunching handle with the door open points to the mechanism. A locksmith guide warns that continuing can leave the door deadlocked shut.
- Do not remove the mechanism or flood the lock with oil. Do not dismantle a multipoint strip if this is your only secure door, and do not spray heavy oil into the cylinder.
The most important rule is the one every guide gives: do not force the handle or turn the key while forcing the handle. Extra force goes through the spindle and gearbox, and a gearbox under load can fail completely, turning a repairable fault into a bigger one.
When it is the gearbox or the mechanism
A failed gearbox usually shows as one or more of these: the handle will not lift or push down at all, it flops with no resistance, it jams halfway, or the handle moves but the locking points do not. The Master Locksmiths Association's guide says a handle that will not lift or go down usually means the gearbox needs replacing, and in some cases the whole locking mechanism does.
Gearboxes and mechanisms are not interchangeable between makes, so a locksmith will often need to identify the manufacturer before ordering a part. Published prices vary. The Master Locksmiths Association's guide says an alignment adjustment should start from about £80, and gearbox replacement is likely to cost from £175 to £335 including labour. A London price list puts a gearbox at £144 to £594. As with every job, ask for a total price before they set off. See what a locksmith costs in London in 2026.
If you cannot lock the door
Do not leave the property with the door unlocked. Ask a neighbour to keep an eye out or stay in until it is fixed, and check your policy, because insurers can make locking doors a condition of cover. If you are locked out because the door jammed shut, see locked out: what to do in the first ten minutes.
Use this repair to improve security
If the cylinder has to be replaced, ask for one tested to TS 007 3 star or Sold Secure Diamond (SS312), measured so it does not stick out past the handle. Changing locks after a burglary explains what those marks mean. If a lock is simply stiff, have it looked at before it fails. Before you book anyone, read how to spot a fake locksmith.
About the author
ESL Locksmiths works from south east London (SE13 and SE6). This page is general advice drawn from published locksmith guides. It cannot diagnose your door, so if you are unsure, ask a locksmith to check.
All advice