Sash Won't Stay Up Only After Balance Replacement: Decision Tree

Why this matters

A double-hung sash that drops on its own after you just replaced the balances is a balance-to-sash matching problem nine times out of ten, and it is one of the few callbacks that is genuinely the tech's setup rather than the homeowner's use. A window balance is a precisely rated spring: it has to counter the exact weight of the sash so the sash floats at any height. Install a balance whose force rating is too light for the sash, mis-engage the balance shoe to the tilt pin, or pair two mismatched balances on one sash, and the sash will sink. Because the symptom appears immediately after the repair, the homeowner correctly points at the work; this tree gets the rating, the engagement, and the cam-lock back to a sash that holds.

Symptom presentation

After a balance replacement, the lower (or upper) sash slowly or quickly slides down from any position instead of staying put. It may drift only when raised high, only on one side, or it may slam shut. Sometimes the sash also tilts or cocks to one side as it falls, indicating one balance is doing more work than the other. The repair is recent and the failure is consistent, which separates this from an old, gradually weakening balance.

Quick checks

Confirm the balance type and rating before touching the shoes again.

Identify the balance system: constant-force (coil), block-and-tackle (string/spring in a channel), or spiral (tube). The diagnosis and the fix differ by type. Read any markings on the replaced balance for force rating, length, and travel.

Weigh or estimate the sash and compare to the balance rating. The balance force must match the sash weight within the manufacturer's window; a balance rated lighter than the sash will not hold it. If you fitted a generic balance "close enough," this is the likely cause.

Check left/right match. Both balances on a sash must be the same rating and type. A sash that tilts as it falls is the tell that one side is mismatched or one shoe is not engaged.

Verify tilt-shoe/pivot engagement. On a tilt double-hung, the sash pivot pin must seat into the balance shoe cam and the shoe must be locked (not in the unlocked/tilt position). A shoe left unlocked, or a pin that did not capture the cam, lets the sash slide free of the balance entirely.

Isolation tree

Branch on weight match, engagement, and symmetry.

Sash drops straight down, both sides, immediately. Force rating too light, or balances installed but not actually carrying the sash. Re-confirm the rating against the sash weight, and confirm both balances are engaged and locked to the pivots. Under-rated balances are the leading cause of a fresh-install drift.

Sash tilts/cocks as it drops. Asymmetric problem: one balance is a different rating, one shoe is unlocked, or one pivot did not seat. Operate each side: lift the sash and watch which corner falls first; that side is the weak or disengaged one.

Sash holds low but drops from high (constant-force/coil specific). The coil may be the wrong travel/length for the sash height, or the coil mounting clip slipped so the spring is not fully developed over the travel. Inspect the coil routing and clip.

Block-and-tackle: sash drops and you hear the cord retract loosely. The balance spring is wrong-rated, the cord slipped off the pulley/sheave, or the take-out clip/attachment to the sash is not hooked. Inspect the cord tension and the sash attachment.

Spiral balance: sash drops and the tube spins freely. The spiral was not pre-tensioned (charged) the correct number of turns for the sash weight, or the tip/U-channel did not engage the sash bottom. Spiral balances must be tensioned to spec on install.

Cam-lock/check-rail issue masquerading as a balance fault. If the sash holds at the top but creeps only near the closed position, confirm the meeting-rail lock and the sash-jamb friction; rarely the balance is fine and a binding or worn jamb liner is the variable.

Confirming diagnosis

Prove it before re-ordering parts.

Force-rating mismatch: with the sash unlocked from the tilt position and set at mid-height, release it. A correctly rated, fully engaged balance pair holds the sash within the manufacturer's drift tolerance. If it sinks evenly, the rating is too light or both sides are disengaged.

Engagement fault: visually confirm each pivot pin is captured in the shoe cam and each shoe is in the locked position. A shoe in the unlock/tilt detent will release the sash; rotating it to lock should restore hold.

Asymmetry: lift one corner at a time. The side that cannot hold its corner is the mismatched or disengaged balance.

Spiral charge: count the pre-tension turns against the manufacturer's chart for the sash weight; an under-charged spiral confirms the drift.

Remediation

Wrong rating: replace with the correctly rated balance for the measured sash weight and the correct length/travel for the sash height, in a matched pair. Do not split the difference with a generic balance; order the rating the sash actually needs.

Engagement: seat each pivot pin into the shoe cam, rotate the shoe to the locked position, and confirm both sides are captured before reinstalling the sash. Re-tilt and re-seat to verify capture.

Spiral balance: re-charge to the specified number of turns for the sash weight, engage the tip into the sash channel, and verify hold across full travel.

Block-and-tackle: re-route the cord over the sheave, hook the take-out clip to the sash correctly, and confirm tension; replace a wrong-rated spring with the matched part.

Constant-force coil: install the correct travel/length coil for the sash, route and clip per the instructions, and verify it develops force across the full lift. After any fix, cycle the sash several times and confirm it holds at low, mid, and high positions on both sides.

References

• AAMA/WDMA/CSA 101/I.S.2/A440 (NAFS), North American Fenestration Standard. Operating-force and sash-balance performance requirements for hung windows.
• AAMA 902, voluntary specification for sash-balance performance and testing (force rating and durability basis).
• IRC R609, Exterior Windows and Glass Doors (window-operation and performance context in the residential code).
• Balance-manufacturer and window-OEM sizing charts (Andersen, Marvin, Pella, Milgard, Simonton, and balance suppliers such as Caldwell): sash-weight-to-balance-rating selection and spiral pre-tension tables.