Window Lock Not Working? Causes and Fixes Explained

A window lock that won't engage is more than an inconvenience — it's a security gap, and often it happens without much warning. One day the handle turns and the window locks shut as normal, the next it doesn't quite catch, or the key won't turn at all. Here's what's usually behind it and what's involved in getting it sorted.

How window locks actually work

Most uPVC casement windows use an espagnolette mechanism — a strip of metal running around the inside edge of the sash with shootbolts that drive out into keeps on the frame when the handle is turned or lifted. Some also have a separate key-operated lock (often a small cylinder in the handle itself) as an additional layer of security.

When people say the 'window lock' isn't working, it's usually one of these two systems — the handle-operated espag mechanism, or the separate key lock — and the fault is often in a different place to what you'd expect.

Handle turns but shootbolts won't engage

If the handle moves freely but nothing seems to happen at the edges of the window, the espag mechanism itself has often worn or seized internally, especially if it's never been lubricated. Years of opening and closing wears the gearing inside, until eventually it stops driving the bolts even though the handle still moves.

Sometimes it's simpler than that — the keeps on the frame have shifted slightly, or the window has dropped a couple of millimetres on its hinges, so the bolts are trying to engage keeps that are no longer perfectly lined up. Our window won't open or close guide covers the alignment side of this in more detail, since the same misalignment causes both symptoms.

Handle is stiff or won't lift fully

A stiff handle that won't lift all the way is often an early sign the mechanism is starting to bind, before it fails completely. Left alone, this tends to get worse rather than better, and forcing it is a common way handles snap off entirely.

Lubricating the mechanism (a spray silicone lubricant on the visible parts of the espag strip, not oil, which attracts grit) sometimes buys a bit of time, but if the stiffness has developed gradually it usually points to wear that a spray alone won't fix long-term.

Key-operated lock won't turn

Where a window has its own key lock — common on ground floor windows and those covered by insurance policies requiring locking windows — a seized or worn lock barrel can leave the key stuck or turning without effect. This is usually a straightforward lock replacement rather than anything to do with the wider mechanism.

If the key has been lost, a locksmith-style replacement of the barrel (rather than the whole handle) is often possible, avoiding the need to change window furniture that otherwise matches the rest of the house.

Timber and aluminium windows

Timber casement windows more commonly use surface-mounted espagnolette bolts or separate casement stays and locks rather than a concealed multipoint mechanism, so faults tend to be visible — a stiff or rusted bolt, a loose keep screwed into the frame, or swollen timber (see condensation and general seasonal swelling issues) preventing the sash from sitting square enough for the lock to catch.

Aluminium windows use similar multipoint mechanisms to uPVC in most cases, so the same gearbox-wear and alignment principles usually apply, just with different part sizes.

Why it's worth fixing promptly

A window that looks shut but isn't actually locked is one of the more overlooked security gaps in a home, particularly at ground floor level or on windows accessible from a flat roof or extension. Beyond security, an unlocked window also seals less well against draughts and rain, so a lock fault can quietly increase heat loss even while the window appears closed.

Call Mark on 07535 916982 or request a callback.