How do I replace a window restrictor?

A restrictor is a small part doing a serious job. Replacing one is straightforward; buying the wrong type or fixing it into thin plastic is where it goes wrong.

Safety

What you'll need

• The old restrictor, or a clear photograph of it
• Screwdriver and possibly a small drill
• Replacement of the same type and fixing centres

Step by step

1. Identify the type first.Cable restrictors use a short steel cable between frame and sash. Hinge restrictors are built into the friction hinge. Some are a separate arm or a lockable stay. They are not interchangeable.
2. Photograph it before removing anything.Both halves in position, plus a shot with a tape measure across the fixing centres. It is far easier than reconstructing the arrangement from memory in a shop.
3. Measure the fixing centres.Distance between screw holes on each plate. Matching these means using the existing holes, which is much stronger than drilling fresh ones nearby.
4. Check the restriction distance.Guidance for child safety is commonly a maximum opening of around 100mm. Buy a restrictor that holds to that, rather than one that merely slows the window.
5. Decide whether you need a key-lockable type.Some restrictors release with a key so the window can open fully for cleaning or escape. Where a window is also an emergency escape route, a releasable type may be required.
6. Check whether it is a hinge fault instead.If the restriction was built into the friction hinge, the whole hinge needs replacing rather than adding a separate restrictor. Get the hinge's stack height and length.
7. Support the sash before removing anything.Particularly on a large or top-hung window. A sash that swings free while you are working can damage the hinge or the frame.
8. Remove the old unit and inspect the holes.Stripped or enlarged holes need dealing with — a slightly larger screw, or a plastic plug suited to uPVC. Screwing into a worn hole gives a restrictor that pulls straight out.
9. Fix into the reinforced section where possible.uPVC frames often have a steel or aluminium reinforcing section inside. Screws reaching it are dramatically stronger than screws in plastic alone.
10. Use the longest screws that fit.Short screws in thin plastic are the reason restrictors fail. Long enough to grip properly, short enough not to break through the frame or foul the sealed unit.
11. Check the alignment before final tightening.Close the window and confirm the restrictor sits square and does not foul the seal. A misaligned one wears rapidly and stops the window closing properly.
12. Test it hard.Push the window firmly against the restrictor, as a child leaning on it would. A gentle test proves nothing. If it flexes or the fixings move, it is not doing its job.
13. Check the others while you are there.Restrictors on other upstairs windows are the same age and have had the same use. Ten minutes checking them all is worth doing.
14. Keep the window locked if you cannot fit it now.An unrestricted upstairs window is a serious hazard. Lock it closed and keep the key out of reach until the replacement is fitted.

Tips

• Photograph it and measure the fixing centres before you buy. The types are not interchangeable.
• Screws long enough to reach the frame's reinforcement are what make it hold.
• Test by pushing hard. A restrictor that passes a gentle test can still fail a real one.

Common mistakes

• Removing a broken restrictor and leaving the window usable — An unrestricted upstairs window is a serious fall risk for a child. Lock the window shut until the replacement is fitted.
• Reusing stripped screw holes — The screws feel tight but grip almost nothing, so the restrictor pulls out under exactly the load it exists to resist.

If it doesn't work

Questions people ask