Why does my window handle turn without locking anything?

A uPVC window locks by a long metal strip in the edge of the sash, with cams that engage keeps on the frame. The gearbox in the middle of that strip converts the handle's quarter turn into the strip's sliding movement, and it is a small casting that eventually rounds off.

What you'll need

• A replacement espagnolette to match
• A Pozidriv driver
• A tape measure
• A camera or phone for the old part

Step by step

1. Isolate the fault.Remove the handle. Turn the square hole in the gearbox with a screwdriver or a spare spindle. Cams move means handle problem; cams do not move means gearbox.
2. Check the handle spindle first.A spindle that has rounded off, or a grub screw that has slipped, gives exactly the same symptom for a fraction of the cost. Look at the spindle's corners for wear.
3. Open the window and find the strip.The espagnolette runs the full height or width of the sash edge, held by screws every 200mm or so, with the gearbox roughly in the middle where the handle is.
4. Photograph everything before removal.Cam positions, which way up the gearbox sits, the position of any shootbolt extensions. It is very easy to refit a new strip a cam-height out.
5. Measure four things before ordering.Overall length of the strip; the backset from the front face of the faceplate to the centre of the spindle hole, usually 20mm or 22mm; the faceplate width, usually 16mm; and the distance from the gearbox centre to each end.
6. Note the cam type.Mushroom cams, roller cams and hook bolts behave differently in the keeps. Replacing mushroom with roller means the keeps no longer compress the sash properly.
7. Undo the strip.Remove every screw along the faceplate and ease the strip out of the groove. It will be stiff after twenty years in a channel full of dust.
8. Clean the channel.Vacuum and wipe. Grit in the groove binds the new strip and is a common reason a replacement feels stiff from the first day.
9. Fit the new strip closed, not locked.With the cams in the unlocked position and the sash open, so nothing is under load while you start the screws.
10. Test before tightening fully.Fit the handle, turn it through its full travel, and watch every cam move. Then tighten the faceplate screws.
11. Adjust the keeps if the cams are close.A new strip may present cams a fraction differently. Most keeps have slotted holes and can move a millimetre or two.

Tips

• The gearbox alone is sometimes available separately for common systems, and swapping it is quicker than the whole strip. It is worth asking a supplier before buying the full espagnolette.
• Universal replacement espags exist and are cut to length on site. They are a good answer for a discontinued system.
• If you snap the handle by forcing it, that is a symptom rather than the cause — the gearbox was already stiff.

Common mistakes

• Buying by overall length alone — Backset and faceplate width decide whether the strip fits the groove and whether the handle spindle reaches the gearbox at all. A strip the right length with the wrong backset will not operate.
• Forcing a stiff handle rather than investigating — Stiffness is friction somewhere in the strip, usually a dry channel or a misaligned keep. Forcing it applies the whole leverage of the handle to a small zinc casting, which is exactly how gearboxes shear.

If it doesn't work

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