Spring Broken But Door Balances Decision Tree

Why this matters

A customer reports a broken torsion spring but, surprisingly, the door still operates and tests reasonably balanced. The conclusion that "only one spring needs replacement" is the most expensive mistake a homeowner can make in this situation. Dual-spring systems share load roughly evenly between the two springs; when one breaks, the other is also at end-of-cycle life and will break within months, leaving the customer with a second emergency call and a door they cannot open in the interim. Single-spring systems with a "broken but balanced" report are usually misdiagnosed; the spring is fatigued and missing a coil, but the door is balanced by the residual partial spring force plus the opener compensating with extra force, masking the real condition. The branches below resolve which scenario applies and what the right replacement scope is.

Symptom presentation

Read the spring system. A dual-spring door has two clearly distinct springs mounted on the same shaft, one to the left of center, one to the right. A single-spring door has one spring mounted on a single shaft (rare in modern residential, more common in older lightweight doors).

Inspect the broken spring. A clean break with the two halves still on the shaft confirms one spring has snapped. A spring with visible coil-to-coil gap (where one coil has separated from its neighbor) indicates a less-obvious failure called "spring sag" that lets the system limp along until the next stress event.

Pull the emergency release and operate the door by hand. Note the door's behavior. A door that lifts easily and holds at any position with one spring broken has been compensated for by an opener that is overdriving; the door is not actually balanced. A door that lifts but feels heavy is closer to honest; the surviving spring is doing most of the work.

Quick checks at the door

Weigh the door. Use a luggage scale at the bottom rail, lift slowly, and read the force required. A residential sectional door weighs typically 130 to 250 pounds depending on size and material. The two springs in a dual system should together provide lift equal to the door weight; one spring alone provides about half.

Read the spring data. Stamped on the side of the spring or on a stamped cone are values for wire size, inside diameter, and overall length. For a dual-spring system, both springs should match. Take photos of both spring data stamps for the order; cone replacement requires matching the existing spring.

Cycle the door once by hand with the broken spring still in place. Note the lift effort, the holding behavior at half-travel, and the resistance to close. A door that drops freely when released has too little spring; a door that rides up has too much. A door that holds within 1 inch of release after 30 seconds is balanced.

Isolation tree

Branch 1 - dual-spring system, one broken. Replace both springs as a matched pair. The surviving spring is also at end-of-cycle life (typical spring rated for 10,000 cycles; a 7-year-old door has consumed most of that capacity) and will break within months. Quote both springs; do not replace only the broken one without a clear documented note that the homeowner declined the second replacement against the company's recommendation.

Branch 2 - single-spring system, broken with door appearing balanced. The remaining spring is providing partial force. Look for spring sag (coils separating from each other), broken or weak end loops, or a spring length that has elongated from years of cycling. Replace the spring with a properly sized new one.

Branch 3 - dual-spring system, one broken, homeowner refuses to replace both. Quote both, document the recommendation, and replace only the broken one if the homeowner insists. Note in the file that the second spring is anticipated to fail. The opener will overdrive to compensate, accelerating wear on the gearbox.

Branch 4 - spring appears intact but the door is unbalanced and drops. A spring may be present but have lost tension from coil separation or from a slipped winding. Inspect the winding cones; a cone that has shifted on the shaft has reduced the spring's preload. Re-wind to the correct turn count for the door per the spring manufacturer's chart.

Branch 5 - spring is broken and a previous repair has compensated by adjusting the opener's force. The opener is doing what the spring should be doing. This is unsafe (the opener cannot do this forever, and the closing force is now elevated to a point where the safety reversal may fail). Replace the spring properly and reset the opener's force limits to spec.

Confirming diagnosis

The manual operation test is the most diagnostic check. A balanced door lifts and holds with light hand force across the full travel; an unbalanced door betrays its condition immediately. Run the test before quoting the work.

For spring data, verify wire size (typically 0.207 inch to 0.250 inch for residential), inside diameter (typically 1.75 to 2 inch), and length (varies by door weight, typically 24 to 38 inches). Order replacements that match exactly; aftermarket springs vary in load rating even when dimensions appear identical.

For dual-spring failure prediction, check the cycle count. Most residential springs are rated 10,000 cycles. A door used 4 times daily has consumed about 1,460 cycles per year; at 7 years it is at about 10,000 cycles and at end of life. A 15-year-old door is well past it. Cycle history is the strongest predictor of imminent second-spring failure.

Remediation

For broken springs in dual systems (Branch 1), replace both. Use a properly torqued winding bar and follow the spring manufacturer's turn-count chart. After install, weigh the door at multiple positions and confirm balance within manufacturer spec.

For broken springs in single systems (Branch 2), replace the spring sized to the door weight.

References

• ANSI/DASMA 102 American National Standard Specifications for Sectional Doors - the standard governing sectional door spring specifications and cycle ratings.
• ANSI/DASMA 116 American National Standard Specifications for Operation and Maintenance for Sectional Doors - the standard for operation, balance, and maintenance.
• UL 325 Standard for Door, Drapery, Gate, Louver, and Window Operators and Systems - the safety standard for opener force-limit and reversal requirements.
• CPSC 16 CFR 1211 Safety Standard for Automatic Residential Garage Door Operators - the federal regulation requiring entrapment protection.
• Manufacturer spring charts and service guides (Clopay, Amarr, Wayne Dalton, Haas, CHI, Service Spring) - OEM spring sizing, cycle ratings, and replacement procedures.