A garage door spring has snapped: what to do, in the right order
A bang from the garage, then a door too heavy to lift. What happened, why you must not lift it, what is safe while you wait, and what the repair involves.
What just happened
A loud bang from the garage — people describe it as a gunshot — and afterwards the door is either stuck, or crooked, or so heavy that it will not lift. A torsion spring has broken. It was wound to hold the whole weight of the door, it has been cycling for years, and the steel finally fatigued at the point where it was most stressed.
A sectional door's spring sits on a shaft above the opening; when it breaks you can usually see the gap in the coil. A tip-up has two side springs, and one snapping leaves the door lifting on one side only, which is why it goes crooked. Either way the door has just gone from weightless to weighing what it actually weighs — sixty to a hundred and twenty kilograms depending on the door.
Do not lift the door
This is the one instruction that matters. A door without its spring is a dead weight on cables and rollers that were never designed to carry it, and lifting it by hand puts that weight on your back and, if it slips, on whatever is beneath it — a car, a foot, a child. A tip-up with one spring gone can swing unpredictably. The motor should not be run either: it will try, stall against its force limit, and if the limit was set too high it will strip its gear or burn out trying.
If the car is inside and you need it, that is a reason to call rather than a reason to lift. A technician can free a door safely in minutes; a household lifting a hundred-kilogram panel cannot.
What is safe to do while you wait
Leave the door where it is. If it is partly open and you are worried about security, a padlock through the track above a roller stops it being lifted from outside. If it is closed, it is closed — a door with a broken spring is very hard to open from outside, which is the one small mercy of the fault.
Do not pull the red release cord. On a sprung door that cord makes the door hand-operable; on an unsprung door it disconnects the only thing holding it up.
Note which spring broke if you can see it, and whether there is one spring or two. Two-spring doors should have both replaced together — the other is the same age and has done the same cycles — and a technician arriving with the right pair saves a second visit.
What the repair involves
A spring replacement is a technician's job, not a homeowner's. The spring is wound to tension with winding bars, and a spring let go carelessly can break an arm. The technician measures the old spring, fits one of the same wire size and length, winds it to the door's weight, and then checks the balance: a door that stays where you leave it at knee height and at head height is correctly sprung. The cables and rollers are checked at the same time, because a spring that snaps often leaves a cable off its drum.
Sectional torsion springs are quoted by size; tip-up side springs are quoted as a pair. Neither is a reason to replace the door, and neither is a reason to replace the motor, though a motor that was run hard against the unsprung door is checked before it is trusted again.
Why it broke, and when it will again
Springs are rated in cycles — ten thousand is the common domestic rating, which is about seven years of ordinary use and two or three years on a busy household or a student let. A spring that has been rusting on the coast breaks sooner. A spring on an unbalanced or sticking door breaks sooner still. If the door is used heavily, a higher-cycle spring costs a little more and lasts several times as long, and the technician will say if that is worth it for yours.