The sash — the framed part that holds the glass — is heavier than it looks, and you never notice because the balance does the lifting. When the window starts sliding down on its own, or crashes shut the moment you let go, the balance has quit. The good news: balances are wear parts, they're cheap, and every type fails in a way you can see once you know where to look.
Look in the side jambs. Open the window and look at the channels on either side of the sash. A round metal tube running vertically, often with a colored plastic tip at the bottom, is a spiral balance — common on aluminum and many vinyl windows.
Check for a channel with a cord. A rectangular metal channel in the jamb, with a cord and a small clip that hooks into the sash, is a block-and-tackle balance — the standard on most modern vinyl windows. A number stamped on the channel (like 2730) encodes its length and strength.
Older house? Look for a rope. If you see a rope or chain running over a pulley at the top of the frame, disappearing into the wall, you have the original system: cast-iron weights inside the wall pocket, tied to the sash with cord. The cord is almost always what broke.
Spiral balance — try tension first. The spiral rod inside the tube winds up to counter the sash weight, and over years it loses a turn or two. With a spiral balance charging tool (a few dollars, or bent from stiff wire in a pinch), hook the rod's end at the bottom of the tube, detach it from the shoe, and add one or two clockwise quarter-turns of tension. Reattach and test. Both sides get the same number of turns — uneven tension makes the sash rack and bind. If the window now creeps up on its own, you went too far; back off a quarter-turn. If the tube is bent or added tension changes nothing, replace the pair — the color of the tip tells you the weight rating to order.
Block-and-tackle — replace the pair. These are sealed units; when the spring or cord inside lets go, you don't rebuild them. Unhook the clip, tilt or lift the sash out (many tilt in for cleaning, which makes this easy), unscrew the channel, and match the stamped number exactly when ordering. Always replace both sides together — a new balance paired with a tired one lifts crooked and wears the new one out early. If the sash popped off its pivot shoes during the failure, check the shoes in the jamb track too; a cracked shoe is a five-minute swap while you're in there.
Weight-and-cord — replace the cord. The weights almost never fail; the cotton cord rots and snaps, usually right at the knot. Access is through a small panel in the jamb (sometimes painted shut — score the paint line with a utility knife) or by removing the interior trim. Fish the weight out, tie on new sash cord — the kind with a braided core, sold for exactly this — thread it over the pulley, and knot it to the sash at the same point as the surviving side. A window with one new cord and one 40-year-old cord will need this job again soon, so do both sides while the trim is off.
A healthy balance holds the sash wherever you leave it — top, middle, three inches from the sill — with no drift for a full minute. The sash should lift with light two-finger pressure and move without tilting. If it drifts down slowly, add a touch more tension (spiral) or confirm you ordered the right weight code (block-and-tackle). Slow drift down on a brand-new balance usually means the strength rating is one step too light for a sash that gained weight — insulated glass retrofits do exactly that.
While the sash is out, this is also the moment to deal with its other complaints. A sash that sticks and scrapes is a different failure with a different fix — see our guide to fixing a sticky window — and a torn screen is a quick job while the window is apart, covered in replacing a torn window screen.
Sometimes the balance is fine and the sash has simply popped off its pivot pins — usually after someone tilted it in for cleaning and didn't reseat it. The window then slides, binds, or drops on one side. Reseating the pins in the shoes costs nothing, so check before you order parts. At the other extreme, if the sash frame itself is rotted or the jamb is falling apart, you're past balance repair and into window repair or replacement — a judgment call that pairs with the sticking-frame diagnosis in our sticking door guide, since the rot and racking logic is the same.
Living with a prop stick is the classic one — it's a security hole and a guillotine waiting for a bump. Tensioning only the side that looks broken guarantees a racked sash. Ordering block-and-tackle balances by window size instead of the stamped code gets you the wrong strength about half the time. And painting over the access panel screws on an old window turns your next cord replacement into trim removal.
Identify the balance, and the repair is already decided: re-tension or replace a spiral, swap a block-and-tackle pair by its stamped number, or re-cord the weights. All three are under-$30, under-an-hour jobs with parts any hardware store stocks or ships. Just prop the sash before you start — gravity is the only real hazard in this repair.
Doing it yourself, typically $10–$30 per window: a pair of block-and-tackle balances, a spiral balance, or a length of sash cord all land in that range. A handyman will usually charge a service call plus parts, so several failed windows in one visit is the economical way to hire it out.
The balance is weakened but not dead — a spiral that's lost tension, or a block-and-tackle spring near the end of its life. Slow drift is your early warning. Fix it on your schedule now, or it will eventually let go all at once.
As a temporary measure, sure — people have done it for a century. As a permanent one, no: the prop can be knocked out from outside (a security problem on ground floors), and a falling sash can break glass or fingers. The real repair is cheap enough that the stick isn't worth it.
You over-tensioned the spiral balance. The spring is now stronger than the sash is heavy, so it wins. Back off a quarter-turn at a time on both sides, evenly, until the sash stays where you leave it.
It varies with use and sun exposure, but roughly 10–20 years is common for modern balances — which is why windows of the same age tend to fail in the same few years. The weight-and-cord system in an old house outlasts everything; only its cord is a wear item.