How to Replace Sash Window Cords

Broken cords are a common reason a sash becomes heavy, drops or will not stay open. Before any work, check whether the sash can be safely supported and whether the counterweights are accessible.

Before starting

Identify the window type, inspect the staff and parting beads, and consider the age of painted surfaces. Old coatings may contain lead. Sashes and concealed weights can be unexpectedly heavy; do not attempt removal without appropriate support and competence.

General repair sequence

A competent repairer typically removes the retaining beads, supports and removes the sash, opens the weight pockets, renews suitable sash cord and rebalances the window before reinstating the beads. The exact sequence varies with the case construction and previous repairs.

When to get help

If the sash is large, glazing is fragile, paint may contain lead or the case is decayed, seek professional assistance rather than forcing components apart.

What the cord does

Traditional box sash windows use a cord running over a pulley to connect each sash to a concealed counterweight. A broken cord means the sash is no longer correctly balanced, so it may feel heavy, drop or twist as it moves. Both sides of the sash should be considered, even when only one cord has visibly failed.

Recognising the fault

Look for a loose or missing cord at the sash stile, uneven movement, a sash that drops on one side, or a weight that can be heard moving freely in the box. Paint buildup and seized pulleys can create similar symptoms, so diagnosis matters before parts are ordered.

Tools and materials to identify

A repair may call for correctly sized sash cord, appropriate fixings, access to the weight pockets, bead removal tools and protective materials for the glass and finishes. Cord diameter and material must suit the pulley groove, sash weight and installation. Do not assume every window uses the same specification.

Repair sequence in principle

A trained repairer secures the sash, removes the necessary beads without damaging them, takes the sash out safely, accesses the weight pockets, renews and secures the cords, then reinstates the sash and checks its balance. Heavy sashes and free-moving weights present trapping and falling hazards. This outline is not a safe substitute for hands-on instruction.

Common mistakes

Replacing one cord without checking the other, using an unsuitable cord, allowing a weight to fall inside the box and reassembling with beads too tight can all create repeat failures. Painted-over access pockets should be opened carefully to preserve historic fabric.

When to call a joiner

Seek professional help for large or high-level sashes, unstable glazing, suspected lead paint, rotten pulley stiles, missing weights or listed buildings where the work could affect protected features.