uPVC Door Won't Lock? Common Causes and How to Fix Them

If your uPVC door won't lock when you lift the handle, the cause is usually one of three things: the door has dropped or moved so the hooks and bolts no longer line up with the keeps, the gearbox inside the multipoint mechanism has failed, or the cylinder cam has worn or snapped. Most are repairable the same day without replacing the door.

Key takeaways

• A handle that is stiff to lift usually points to alignment. A handle that feels floppy or does nothing usually points to a broken part inside the lock.
• You can safely check the keeps, the hinge adjustment and lubrication yourself. Do not force the handle or the key.
• Replacing just the gearbox is often enough. A full multipoint replacement is needed when several components are worn or the strip is damaged.
• Any repair is a good moment to upgrade the cylinder to a TS007 3-star or Sold Secure SS312 Diamond rated one.

How a uPVC multipoint lock works

Most uPVC front and back doors in London homes use a multipoint lock. A long metal strip runs down the locking edge of the door, with a central gearbox behind the handle and several locking points above and below it. These can be hooks, rollers, mushroom cams or shoot bolts, depending on the make.

Lifting the handle drives those locking points into the keeps on the frame. Turning the key then rotates the cylinder cam inside the gearbox and throws the central deadbolt. Because handle, gearbox, cylinder and keeps all work together, a fault in any one of them produces the same symptom: the door won't lock.

Common reasons a uPVC door won't lock

1. The door and keeps are out of line

This is the most frequent cause we see. Over time the locking points stop meeting the keeps squarely. You will notice the handle getting harder to lift, or needing a shove or a pull on the door before it will go up. If it carries on, the extra strain is passed straight to the gearbox, which is how a simple alignment problem turns into a broken mechanism.

2. The door has dropped on its hinges

uPVC doors are heavy, and the hinges settle with use. When a door drops, the bottom corner on the lock side scrapes the threshold and the hooks sit lower than the keeps. Most modern uPVC doors use adjustable flag hinges, which can be set for height, side to side position and compression against the seals, usually with an Allen key.

3. A failed gearbox or multipoint mechanism

The gearbox contains small springs and moving parts that wear out. When it fails you may find the handle lifts but nothing engages, the handle will not return to horizontal, or the key will not turn even with the handle fully up. Searches like "upvc door mechanism repair" are usually about this fault. If you look along the edge of the door with it open and the locking points do not move when you lift the handle, the gearbox is the likely culprit.

4. A broken handle spring cassette (the floppy handle)

A uPVC door handle that droops or flops down instead of springing back to horizontal often has a broken spring cassette inside the handle itself. This is a cheaper fix than a gearbox, because only the handle set needs replacing. If the replacement handle is still floppy, the return spring in the gearbox has gone instead, so it is worth having both checked at the same visit.

5. A worn or snapped cylinder cam

If the key turns but the door won't open, or the key spins round without locking anything, the cam on the back of the cylinder may be worn or broken. The cam is the small lever that turns the gearbox. Once it has snapped, the key is no longer connected to the mechanism. The fix is a new cylinder, measured to the correct size for your door.

6. A seized mechanism

Mechanisms that have never been lubricated, or that face driving rain, can stiffen until the handle barely moves. Caught early, cleaning and lubrication can free it. Left too long, the internal parts wear and need replacing.

7. Swelling and expansion in hot weather

uPVC and composite doors expand in heat, especially darker coloured doors and those in direct afternoon sun. A door that locks fine in the morning but sticks by mid-afternoon is a classic sign. A small adjustment to the hinges or keeps usually solves it, so the door has enough clearance through the warmer months.

Symptoms, likely causes and fixes

What you can safely check yourself

A few simple checks can save you time. None of them involve taking the lock apart.

1. Test the lock with the door open. Lift the handle and turn the key while the door is open. If everything moves smoothly, the mechanism is probably fine and the problem is alignment. If it is still stiff or nothing moves, the fault is inside the lock.
2. Look at the keeps. Check the frame for scuff marks around the keeps, which show where the hooks or rollers are catching. Some keeps have adjustment screws that let you move them slightly. Loosen, move a millimetre or two, retighten and test.
3. Check whether the door has dropped. Look for rubbing on the threshold or an uneven gap along the top of the door. If your hinges have visible adjustment points, small turns with the correct Allen key can lift the door back into line. Make one small change at a time and test after each.
4. Lubricate the locking points. With the door open and the mechanism in the locked position, apply a light machine oil or a PTFE spray to each hook, roller and bolt along the edge. Operate the handle several times. For the keyhole, use a lubricant made for lock cylinders rather than household oil, which can attract dirt.
5. Swap the handle if it is only floppy. If the handle is the only problem and you are comfortable measuring the spindle and screw centres, a new handle set is a reasonable DIY job.

Regular lubrication and adjustment is exactly what our door and lock maintenance service covers, and it is the simplest way to stop a small fault turning into a broken gearbox.

When not to force the handle

Leaning on a stiff handle or turning the key harder is tempting. Please don't. The handle and cam act as levers on the gearbox, and forcing them is how a cheap adjustment becomes a full lock replacement.

• If the handle needs real effort to lift, stop and check alignment instead.
• If the key will not turn, do not use pliers or a tool through the key bow. A snapped key inside the cylinder makes the job harder.
• If the door is locked shut and the key spins, do not try to drill or prise the door. You can damage the frame, the seals and the glazing, all of which cost far more than the lock.
• If the handle has stayed down in the locked position and will not lift, leave it and call for help.

How a locksmith diagnoses and repairs a uPVC door lock

When one of our engineers arrives for a uPVC door lock repair, the first job is working out whether the problem is the door, the lock or both. That normally means checking the hinges and keeps, testing the mechanism with the door open, and if needed removing the cylinder and the strip to inspect the gearbox and locking points.

Gearbox replacement or full multipoint replacement

If the gearbox is the only worn part and the rest of the strip is in good condition, replacing the gearbox alone is usually the sensible option. It costs less than a full mechanism and the door keeps its original locking points. We match the replacement to your existing lock, which means identifying the make, the backset and the spindle and cylinder centres.

A full multipoint strip replacement makes more sense when several locking points are damaged, the strip is bent or corroded, or the lock is an older or discontinued type where a matching gearbox is not available. Our engineers carry common gearboxes and mechanisms, and we will explain the options and give you a firm price before any work starts. You can read more about how we handle these jobs on our uPVC door repair page.

Upgrading the cylinder while the lock is open

Many older uPVC doors still have basic euro cylinders, which are vulnerable to snapping. If the cylinder is coming out anyway, it is worth considering an upgrade. A cylinder rated to TS007 3-star on its own, or a TS007 1-star cylinder paired with 2-star security handles to reach a combined 3-star rating, gives much better resistance to snapping, drilling and picking. A cylinder certified to Sold Secure SS312 Diamond is tested to a high level against common attack methods. Both are widely recommended for front doors. We will also check that the cylinder does not stick out too far from the handle, which matters for anti-snap protection.

If your door is stuck open or stuck shut

A door that will not lock at night, or will not open in the morning, needs a different approach from a door that is just stiff.

• Stuck open (won't lock): close it as far as you safely can, secure any other doors and windows, and move valuables away from the entrance. If it is an external door, do not leave the house empty. Call an emergency locksmith who can repair the mechanism or make the door secure on the same visit.
• Stuck shut (won't open): check whether there is another way in or out of the property. Do not attack the door or the frame. A locksmith can usually open a uPVC door with a failed mechanism and then repair or replace the parts.

We work 24/7 across London, with typical arrival in 20 to 30 minutes, so you are not left with an insecure home overnight.

How much does a uPVC lock repair cost?

The price depends on what has failed. An adjustment costs less than a gearbox, and a gearbox costs less than a full multipoint mechanism. As a guide, lock replacement is typically £120 to £200 including parts and labour, and most of our jobs fall between £89 and £300 depending on what is needed. There is no separate call-out fee. Out-of-hours call-outs may carry an extra charge, and we always confirm a firm price before any work starts. All repairs come with our 180-day parts and labour guarantee, and the work is carried out by DBS-checked engineers. Full details are on our prices page.

Need your uPVC door lock repaired?

If your uPVC door won't lock, the handle has gone floppy or the key turns without opening the door, call Locksmith24. We will diagnose the fault, explain whether a simple adjustment or a new part is needed, and get your door locking properly again. You can also contact us to book a visit at a time that suits you.

Frequently asked questions