Replace a broken sash cord by removing the bead, lifting out the sash, and fitting new cord to the weight.
SC-01Set up and identify the faultLay a dust sheet under the window. Open the sash fully and look for the loose, sagging cord — this tells you which side and which sash (upper or lower) needs work. Check whether the staff bead has been painted over, as this affects how easily it comes free.
SC-02Score the paint and remove the staff beadRun a craft knife along the paint line where the staff bead meets the frame, to stop the paint tearing. Ease the bead away with a flat bar or old chisel, starting at the top and working down. Keep the bead in one piece — you'll refit it later.
SC-03Lift out the sashWith the bead free, tilt the sash out of the frame towards you and lift it clear. If the broken cord is still attached, cut it now to release the sash. Lean the sash somewhere padded and out of the way — it's heavier than it looks.
SC-04Open the weight pocketFind the pocket piece low down on the inside of the sash box — a rectangular panel, usually screwed or nailed in place. Remove the screws with a screwdriver, or gently lever nailed pockets with a chisel, and pull the piece free to expose the weight cavity.
SC-05Retrieve the weight and old cordReach into the pocket and lift out the cast iron weight. Untie or cut the old cord from the weight's eye. Pull what remains of the old cord out over the pulley at the top of the box — it can help guide the new cord through.
SC-06Thread the new cord over the pulleyCut a length of new sash cord slightly longer than the old one. Tie a small weight or nail to one end as a lead, feed it over the pulley wheel and let it drop down inside the box until it appears at the pocket. Tie the cord to the eye of the weight with a reef knot.
SC-07Check the weight hangs freelyPull the cord so the weight lifts about 50mm clear of the bottom of the pocket, then let it settle. It should hang straight and not rub against the sides or the other weight. If it catches, check nothing has twisted inside the box.
SC-08Fix the cord to the sashHold the sash in place in the frame, resting on the sill. Pull the cord taut so the weight sits about 50mm below the pulley when the sash is fully closed, then nail the cord into the groove on the edge of the sash using cord tacks — three or four along its length. Trim off any excess cord.
SC-09Test the sash before closing upSlide the sash fully up and down in the frame while the pocket and bead are still off. It should move smoothly with no dragging or twisting cord. If it sticks or the weight bangs the bottom of the box, adjust the cord length now — it's much easier before everything is closed up.
SC-10Refit the pocket piece and staff beadScrew or nail the pocket piece back into place. Refit the staff bead using the same pin holes where possible, tapping panel pins gently home. Don't overtighten the bead — the sash needs a little clearance to slide freely.
SC-11Tidy up and finishOpen and close the sash a few times to check it runs smoothly and holds its position when left half-open. Touch up any chipped paint on the bead. Clear away the dust sheet and dispose of the old cord and weight-cavity debris.