A sash that will not stay put is one of the most common faults on old double hung windows. You lift the bottom sash, let go, and it drops back on your fingers. The window still opens and closes, so people live with it for years, but the fix is usually quick and cheap once you know what has failed.
Only two things hold a sash at the height you leave it: the cords and the pulleys. When a window will not stay open, one of those two has given up. Here is how to tell which, and how to put both right.
Why it slams shut
A traditional double hung window works on a simple balance. Each sash hangs on a pair of cords that run up and over pulleys at the top of the frame, then down inside the boxes on either side to a weight. When the weight matches the sash, the sash floats and stays wherever you leave it.
Break that balance and the sash falls. There are two usual causes:
- A broken cord. Old cotton cord frays and snaps, usually at the top where it bends over the pulley thousands of times. Once a cord goes, the weight drops to the bottom of the box and the sash has nothing holding it up on that side.
- A seized pulley. The pulley wheel stops turning. It might be clogged with old paint, rusted on its axle, or worn. When the wheel will not spin, the cord drags instead of running freely, so the sash sticks, jerks, or will not hold its position smoothly.
Both faults are worth fixing properly rather than propping the window open with a block of wood. A sash that drops is a hazard around small children and fingers, and a jammed pulley makes the whole window hard to use.
Quick diagnosis
You can work out which fault you have in about a minute, without taking anything apart.
- Lift the sash slowly and feel the weight. If one side feels heavy and dead while the other side moves normally, the cord on the heavy side has probably snapped. With a broken cord the sash also tends to sit crooked in the frame.
- Listen and feel at the top. Raise the sash and watch the pulleys. A healthy pulley wheel turns as the cord moves over it. If a wheel sits still while the cord slides across it, or you hear a scrape or squeak, that pulley is seized.
- Check for a cord tail. Look down the gap between the sash and the frame. If you can see a cut or frayed cord end hanging loose, or no cord at all where one should be, that confirms a break.
If both cords are intact and the pulleys spin freely but the sash still will not hold, the balance itself may be off, often because someone has fitted heavier glass without adjusting the weights. That is a separate job, but broken cords and seized pulleys cover the large majority of cases.
Replacing the cord
Replacing a sash cord is a satisfying afternoon job with hand tools. The short version is: ease off the staff bead, lift the bottom sash out, open the pocket in the side of the frame to reach the weight, thread new cord over the pulley and down to the weight, tie it on, then refit the sash with the cord pinned into the groove at the correct length.
We have written the whole thing up step by step, with the knots and the length setting explained, in our guide on how to replace a broken sash cord in a double hung window. It is worth doing both cords on a sash at the same time, because if one cotton cord has failed from age, the other is not far behind.
What you use for the new cord matters more than people expect. Cheap synthetic cord can stretch or slip, and thin cord wears through fast where it runs over the pulley. We fit 6mm waxed cotton sash cord, which grips the pulley well and runs quietly. There is more on the different cord types, and why we settled on this one, in our comparison of the best sash cord for heritage windows and the story behind it on our sash cord page.
Replacing pulleys
If the diagnosis points to a seized wheel, the pulley comes out with the sash already removed. Undo the two screws in the pulley faceplate and lever the whole unit out of its mortice in the frame.
Sometimes a pulley only needs cleaning. Old paint round the edge of the wheel is a common culprit, and a wheel that has stopped turning purely because of paint can often be freed with a little work and a drop of light oil on the axle. If the wheel is worn, cracked, or rusted solid, replace it. New sash pulleys drop straight into the same mortice and take the same two screws, so the swap is quick.
While you have a pulley out, run the new cord over the wheel by hand and check it spins smoothly under a little tension. A worn axle can still drag once the sash weight is on it, so it pays to test before you close everything up.
While the sash is out, seal it
Taking a sash out is the fiddly part of the whole job, so it is the ideal moment to deal with draughts at the same time. With the window apart you can fit brush seals into the staff bead and parting bead runs, and sort out the gap at the meeting rail where the two sashes cross. Doing it now means one lot of disassembly instead of two, and the same removal is covered in our sash cord guide.
One safety note on the weights. In older windows the counterweights are often made of lead, and the surface can leave a fine residue on your hands. Wear gloves when you handle the weights, keep them away from children, and wash your hands before you eat or drink.
FAQ
Can I fix a sash that will not stay open without taking the window apart?
Not properly. The cords and weights sit inside the frame, so the sash has to come out to reach them. The good news is that removal is straightforward with hand tools, and it is the same access you need whether the fault is a cord or a pulley.
How do I know if it is the cord or the pulley?
Lift the sash slowly. If one side feels dead and heavy, or you can see a frayed cord end, the cord has snapped. If the cords look intact but a pulley wheel does not turn as the sash moves, or it scrapes and squeaks, the pulley is seized.
Should I replace both cords or just the broken one?
Replace both on the sash. If one cotton cord has failed from age, the other has had the same wear and will usually go soon after. Doing both at once saves taking the sash out a second time.
What cord should I use?
A good quality 6mm waxed cotton cord grips the pulley and runs quietly, and it holds up far better than thin or cheap synthetic cord. We use 6mm waxed cotton sash cord on our own jobs.
Do I have to replace a seized pulley, or can I just clean it?
If the wheel has only stopped because of paint round the edge, cleaning it and a drop of oil on the axle often frees it. If the wheel is worn, cracked, or rusted solid, fit a new pulley. New units drop into the same mortice and take the same screws.