Why won't my old double-pane window stay open?

What's actually happening

Your window has a counterbalance that offsets the weight of the sash. When it works, the sash floats and stays wherever you leave it. When it fails, gravity takes over and the sash slides shut.

In an older home, the balance type depends on when the window was built. That's the single most important thing to figure out before you buy a part.

The good news: this is one of the most DIY-friendly window repairs there is. The part is cheap, the tools are basic, and you're not touching the glass seal or the frame structure.

The catch is identification. Buy the wrong balance and it won't fit, won't hold, or won't last. Spend ten minutes figuring out what you have first.

Why older windows lose their hold

The most common failure by far is a worn balance, whichever type your window uses. Springs fatigue, cords fray, and coils lose their curl. It's wear, not abuse.

In genuinely old homes, pre-1950, you're likely dealing with rope-and-weight windows. A cotton cord runs over a pulley to a cast-iron weight hidden in the wall. When the cord snaps, the sash drops instantly.

From the 1960s into the 80s, spiral balances took over. These are thin tubes with a twisted rod and a spring inside. They quietly lose tension over decades.

The 90s and 2000s brought vinyl and wood replacement windows into a lot of older homes. These use block-and-tackle or constant-force coil balances that clip into a plastic jamb liner.

Here's the wrinkle that trips people up. If someone put double-pane glass into an old single-pane frame without upsizing the balance, the balance was fighting a losing battle from the start. It'll fail early and keep failing until you match the balance to the actual sash weight.

Match the fix to the era

Getting the era right saves you a wasted trip and the wrong part.

Rope and weight (pre-1950): Look for a round pulley in the jamb near the top of the sash travel and a knotted cord. There's usually an access panel low in the jamb to reach the weight.

Spiral balance (1960s-80s): A slim metal tube in the side channel with a tensioning screw or hook at the top. You re-tension it with a special spiral tool or replace the whole tube.

Block-and-tackle (1990s-2000s): A plastic housing with a visible cord and mini pulley that clips into the track. These pair with tilt-in sashes.

Constant-force coil (1990s-on vinyl): A curled steel ribbon anchored at the top of the channel, like a tape measure spring. Rated by force, stamped on the metal.

• Pre-1950: sash cord and cast-iron weight
• 1960s-1980s: spiral (torsion) balance
• 1990s-2000s: block-and-tackle balance
• 1990s-present vinyl: constant-force coil balance

How to diagnose and fix it step by step

Start with the drop test. Raise the sash halfway and let go slowly. A fast fall means the balance is dead; a slow creep means it's weak but partly working.

Next, expose the balance. On tilt-in windows, unlock the sash, tilt it toward you, and lift it out of the pivot bars. On older wood windows, pry off the interior stop molding with a putty knife to free the sash.

Now you can see the failure. Look for a snapped cord, a slack spiral, a frayed block-and-tackle line, or a coil that won't hold its curl.

Check the other side. If one balance is dead, the matching one is worn too. Replace both.

Measure everything. Balance length, sash width, and where you can, sash weight on a bathroom scale. Coil and spiral balances are rated for a weight range and you must land inside it.

Install the new balances, re-seat the sash on both pivot bars or in both tracks, and test the hold at low, middle, and high positions before reinstalling any stops.

If the sash still won't hold, either the rating is wrong or the jamb liner is worn. Recheck the numbers before assuming the part is defective.

What it costs in 2026

DIY parts run $20–$120 for a pair of balances plus incidentals like sash cord, a spiral balance tool, or new tilt latches. Individual balances are often $12 to $30 each.

A pro repair runs $200–$900 for a typical double-hung, which covers a service call, diagnosis, matched balances, and labor for one to two windows.

The gap is mostly the trip charge and labor. Most companies have a minimum visit fee of $125 to $200 before parts.

If you have several failing windows, batch them into one service call. The per-window cost drops fast once the tech is on site.

Compare that to a full replacement window, which runs $600 to $1,200 installed for a standard double-hung in 2026. Balance repair is the clear win when the frame and glass are sound.

• DIY balance pair: $20–$120 total
• Single balance: $12 to $30 each
• Pro repair, 1-2 windows: $200–$900
• Full replacement window: $600 to $1,200 installed

DIY or call someone

This is a solid DIY job if you can identify the balance and lift the sash safely. Spiral and block-and-tackle swaps on tilt-in windows take most people 30 to 45 minutes once they've done one.

Call a pro if the window is a rope-and-weight system with no access panel, if you'd need to convert it to springs, or if the jamb liner is cracked and needs replacing.

Also call if the glass is fogged. That's a failed seal, and a tech will help you decide between reglazing and full replacement instead of sinking money into a balance.

Lead paint changes the math too. On a pre-1978 wood window that needs sanding, hire someone certified for lead-safe work rather than risking it.

Can this wait?

It's a moderate-urgency fix. Nothing floods or shorts out, but a window that won't stay open has real safety strings attached.

The immediate hazard is the sash slamming shut on fingers or an arm. That's a genuine emergency-room risk, especially with kids around.

If the window is a bedroom egress window, it needs to open and stay open for a fire exit. That moves it up the priority list fast.

Waiting also costs you. One dead balance dumps the whole sash load on the surviving one, so it wears out faster. A single-part fix becomes a two-part fix.

Bottom line: prop it safely if you must, but plan the repair within a week or two rather than living with a dowel all winter.

Safety before you start

Treat the sash as if it will drop, because it will. Prop it with a solid stick before your hands go near the track.

Respect the weight. Cast-iron counterweights and double-pane sashes are heavier than they look, and a slip can pin a hand or crack the glass.

Mind spring tension on spiral balances. The twisted rod stores energy and can spin back if you release it wrong.

Assume lead paint on any painted wood window in a pre-1978 home and don't create dust without containment.

How we diagnose this

We start with the drop test to gauge how much holding force is left, then identify the balance system by era and jamb inspection.

We check both balances every time, because paired wear is the rule, not the exception.

We separate the balance problem from unrelated issues like a fogged seal or a warped sash, so you don't pay to fix the wrong thing.

Cost ranges reflect 2026 US pricing for parts and typical regional service-call minimums, not a single quote. Your number will land inside the range depending on window type and how many you fix at once.