A window that won't lock is a serious security issue, but it's also one of the most common UPVC faults. In most cases, the cause is straightforward and the repair is quick. Here's what's likely causing the problem.
The Window Mechanism Has Failed
The most common reason a UPVC window won't lock is that the espagnolette mechanism — the strip of metal inside the frame that the handle operates — has broken or worn out. When you turn the handle, the mechanism should move up or down, driving locking bolts into keeps in the outer frame. If the mechanism is broken, the bolts won't move. You may be able to see this by watching the bolts (visible at the edge of the sash) as you turn the handle — if they don't move, the mechanism is the likely culprit.
The Handle Spindle Has Snapped
Sometimes the mechanism is fine but the spindle inside the handle has snapped. The handle turns freely without engaging anything. This is actually good news — spindle failure is cheaper to fix than a full mechanism replacement. The handle is removed to confirm the spindle has sheared, and a new handle with an intact spindle is fitted. The mechanism below is usually undamaged.
The Locking Bolts Don't Reach the Keeps
If the mechanism is working but the bolts don't engage with the keeps in the frame, the window may have dropped or moved slightly. Even a 2–3mm misalignment is enough to prevent engagement. Check whether the window closes fully and whether there's any gap around the sash when it's in the closed position. Hinge adjustment or hinge replacement usually brings the sash back into alignment so the bolts engage correctly.
The Keep Has Moved or Is Damaged
Keeps are the small metal plates set into the window frame that the locking bolts engage with. Occasionally a keep works loose or the screw holes strip, allowing it to move. If a keep has shifted even slightly, the bolt won't engage cleanly. Refitting the keep with longer screws or replacing it with a new one is a quick and inexpensive fix. The Glass Guardian handles all window locking faults across Birmingham and the Black Country.
Need a UPVC Repair in Birmingham or the Black Country?
The Glass Guardian provides fast, affordable UPVC window and door repairs across Birmingham, Dudley, Walsall, Wolverhampton, and the surrounding area. Call for a free quote.