Every week we get some version of the same pushback: "Only one spring broke — can't you just replace that one?" It is a completely reasonable question. The spring that snapped is visibly broken; the other one looks fine. Replacing both feels like an upsell. Let us explain why it is not.
Torsion springs are rated by cycle life. A standard residential spring is rated 10,000 cycles — one cycle being one open and one close. If you open the door four times a day, that is roughly 1,460 cycles per year and a seven-year lifespan. Both springs on any given door were installed the same day, wound to the same tension, and have run through the same number of cycles. When one spring has reached its fatigue limit, the other spring has too — it just happened to fail second.
The metallurgy is simple
Steel under repeated cyclic stress accumulates micro-fractures over time. Torsion springs are coiled steel under enormous tension, and each open-close cycle flexes the coil slightly. The fractures propagate invisibly until one spot reaches critical crack length and the spring snaps — usually at a winding cone or a tight coil at one end. The surviving spring is carrying the same total cycles and the same crack propagation history. It is not in better condition; it just has not reached its fracture point yet.
In our experience, when we replace only the broken spring, we are back at the same house within twelve to eighteen months for the second one — which now also means a second service call fee, a second diagnostic, and a second time the car is stuck inside. Replacing the pair in the same visit costs perhaps $80–$100 more than a single spring, and it buys you seven more years of balanced operation.
Balance matters too
Two springs share the load equally when the door travels. If one spring is new (full tension, correct wire diameter) and one is four years old and fatigued (reduced elasticity, slightly deformed coil), the door pulls harder on one side during travel. That lateral imbalance stresses the cables, puts uneven wear on the rollers and track, and can warp the bottom door panel over time. A new door panel runs $220–$900. The spring balance issue is free to prevent.
We do not replace both springs to pad the invoice. We replace both springs because the math is straightforward, the risk of the alternative is real, and we would rather explain it once than see you again at 7 AM when the second spring lets go in January.