Sash Won't Stay Up: Balance vs Spring vs Cord Translation Decision Tree

Why this matters

"The window won't stay open, it slams shut" is a counterbalance failure, but the word covers three different mechanisms across the window types you service. Modern vinyl and aluminum hung windows use block-and-tackle (constant-force coil) or spiral balances; older wood double-hungs use weight-and-cord (or chain) systems. Each fails differently and each needs a different part and procedure. Translating the customer's complaint into the actual balance type before you order parts is what makes this a one-trip repair instead of a two-trip parts chase.

A sash that drops is also a safety issue: a guillotine sash can pinch fingers and, on egress windows, a sash that will not stay open compromises emergency escape per IRC R310. This is not a cosmetic complaint to slow-walk.

Symptom presentation

• "It slams down when I let go," modern vinyl/aluminum hung window: a balance failed (block-and-tackle string broke or spiral balance lost tension).
• "It creeps down slowly," modern window: a balance is weakening or the sash is overweight for the balance (often after a glass upgrade).
• "The cord snapped and I can hear the weight drop in the wall," old wood window: a sash cord/chain broke and the counterweight fell into the weight pocket.
• "Both windows on this wall do it," recent install: possible wrong balance spec for the sash weight, not random failure.

Quick checks

• Identify the window generation. Vinyl/aluminum with a tilt-in sash and a jamb track: modern balance (block-and-tackle or spiral). Wood sash with a parting bead and side jamb pockets: weight-and-cord. This single read forks the entire diagnosis.
• Sash behavior. Lift the sash to the top. Does it hold? Drop in stages? Slam? A sash that holds high but drops low, or one side that drops while the other holds, tells you which balance is failing.
• Side-to-side test. Many failures are one-sided. Lift one bottom corner at a time. If one corner gives and the other holds, you have a single failed balance/cord, not both.
• Modern balance inspection. Tilt the sash in and inspect the balance shoes/clips in the jamb track. Look for a broken block-and-tackle string, a detached balance shoe, or a spiral balance that spins free (lost spring tension).
• Wood window inspection. Listen and probe for a dropped weight in the pocket; open the access plate (or remove the stop) to find the broken cord/chain.

Isolation tree

1. Modern vinyl/aluminum hung window.
   • Sash slams shut, one side: a block-and-tackle balance string broke or a balance shoe detached on that side. Inspect that jamb track.
   • Sash creeps down both sides on a recent install or after a glass change: the balances are underrated for the sash weight (spec mismatch), or both are aging. Verify the balance charge/length against the sash weight.
   • Spiral balance type: if the rod spins with no resistance, the spring tension is gone (broken or unwound). The spiral balance needs re-charging or replacement.
2. Older wood double-hung.
   • Heard a thunk in the wall and the sash drops freely: the sash cord or chain broke and the counterweight fell. The weight is intact in the pocket; the connection failed. This is a cord/chain replacement, not a balance.
   • Sash drops with effort but no thunk: cord stretched or the knot pulled out of the sash mortise, partial failure.
3. Both sashes/both sides on multiple recent units.
   • Pattern points to specification, not random failure. Confirm the installed balance rating matches the actual sash weight (heavy glass packages, triple-pane, or laminated/impact glass change the required charge).

Confirming diagnosis

• Balance (block-and-tackle / spiral) confirmed on a modern window when tilting the sash reveals a broken balance string, a detached shoe, or a spiral that has lost tension, and replacing/re-charging the balance restores hold.
• Spring/charge confirmed specifically when a spiral balance spins freely with no resistance, or when a sash creeps because the balance charge is too light for the glass weight.
• Cord/chain confirmed on a wood window when the counterweight has dropped into the pocket and the cord/chain is broken or pulled from the sash, and re-cording/re-chaining over the pulley restores function.

Remediation

• Block-and-tackle / spiral balance: Replace the failed balance with a unit matched to the sash weight and track. On spiral types, re-charge or replace; do not reuse a balance that has lost tension. Replace balances in pairs where the second is near end of life.
• Spec mismatch: Re-specify balances to the actual sash weight. After a glass upgrade, the original balances may be undersized; install the correct charge so the sash holds at any height.
• Cord/chain: Replace the sash cord (or upgrade to chain) over the existing pulley, re-seat the counterweight, and re-knot/anchor into the sash mortise. Verify the sash holds at top, middle, and bottom and tilts/operates freely.
• After any fix, confirm the sash stays open hands-free at multiple heights, that egress windows fully open and hold per IRC R310, and that the lock and weatherstrip still engage.

References

• International Residential Code (IRC) R310, Emergency Escape and Rescue Openings (egress window operability and clear-opening requirements).
• AAMA / WDMA / CSA 101/I.S.2/A440 (NAFS), North American Fenestration Standard (operating-force and sash performance requirements for hung windows).
• AAMA balance and hardware technical references (block-and-tackle and spiral balance selection by sash weight).
• Manufacturer sash and balance service literature (balance charge/length matched to sash weight and track profile).