uPVC Door Will Not Lock: How to Work Out Why

Nearly every uPVC or composite door that stops locking has one of three faults: a worn multi-point gearbox inside the door, a door that has dropped a couple of millimetres on its hinges, or a tired euro cylinder. You can usually tell them apart in about a minute. Open the door and lift the handle in mid air: if the hooks shoot out cleanly, the mechanism is alive and the problem is alignment. If the handle flops or stops halfway, the gearbox is the suspect. If the key itself will not turn either way, look at the cylinder. Each fault is a part swap, not a new door.

Gearbox failure — the most common cause

Inside every multi-point locking door is a gearbox that drives the hooks, bolts and rollers along the edge of the door when you turn the key or lift the handle. Over years of use this gearbox wears out and stops engaging properly, even though the cylinder and key are perfectly fine.

This is usually a straightforward one-visit repair — the mechanism is unscrewed, swapped for a matching replacement, and tested through several full lock cycles before we leave.

The door has dropped

uPVC and composite doors are heavy, and over time the hinges can allow the door to sag very slightly — often just a couple of millimetres. That's enough to throw the hooks and keeps out of alignment so the lock won't engage cleanly, even though nothing is actually broken.

Adjusting the hinges to lift and square the door back up is often all that's needed, and it's a much smaller job than replacing the lock.

Things worth checking before you call

A few quick checks can save you a callout, or at least tell us what to bring.

• Lift the handle fully before turning the key — most multi-point locks need the handle lifted to engage the hooks
• Check the door isn't rubbing on the frame at the top or bottom — a sign it's dropped
• Look at the keeps on the frame for damage or misalignment
• Note whether the key turns freely with the door open but not when it's shut — this points to alignment rather than the cylinder

When it's the cylinder, not the gearbox

If the key is stiff, won't turn at all, or turns but does nothing, the euro cylinder itself may have worn or seized. This is usually the cheapest and quickest part to replace, and it's a good opportunity to upgrade to a 3-star anti-snap cylinder for extra security at the same time.

A cylinder that only misbehaves with one particular key has often simply worn against a copy cut from a copy. Try the original key before assuming the worst.

What the fault feels like in the hand

Doors give away the cause through feel and sound long before anything is taken apart. Reading those signs correctly is the difference between a part swap and a wasted afternoon.

• Handle rises easily but drops straight back and nothing moves: the gearbox drive has stripped inside
• Handle needs a shoulder against the door to lift: hooks are fouling the keeps, so the door has dropped or the frame has moved
• Loud clunk then free movement: a cam or spring has snapped and the mechanism is now dead
• Locks fine in cold weather, sticks in summer: thermal movement in a dark composite slab, an adjustment rather than a repair
• Locks fine when the door is open, fails when shut: alignment every time, never the cylinder

Getting through the night if it will not lock

If the door cannot be secured, avoid forcing the handle repeatedly, because a half-engaged hook can jam the door in the closed position and turn a simple repair into a forced opening. Lift the handle gently once, and if the hooks stay out, leave them out rather than cycling them again.

Where the door still shuts but will not lock, use any second point of security you already have, such as a nightlatch, a bolt on an inner door or a key-operated patio lock, and keep the door itself closed rather than propped. Note the make stamped on the edge of the mechanism if you can see it, since matching that plate is what lets the correct part arrive on the first visit.

Call Mark on 07535 916982 or request a callback.