The sound is the signature: a bang like a gunshot or a falling toolbox from the garage, and then a door that the opener lifts two inches and gives up on. What happened is mechanical and simple. The torsion spring above the door, the part that counterbalances the door's weight, has snapped, usually at the end of its rated cycle life, and the door has become the dead weight it always was.
New Bedford version: if the spring went in January, you have joined the state's most common winter call, and the cold that broke it is also why you should not run the door on the opener, which will burn out lifting dead weight. Park outside the door's path, keep the door down, and let the replacement be a matched pair with the cables read at the same visit. Salt thinned coils rarely fail one at a time here.
What not to do matters more than what to do. Do not keep pressing the opener button: the motor is now trying to lift hundreds of pounds it was never sized for, and stripped opener gears are the standard second bill. Do not try to wind, clamp, or pry the broken spring. And do not lift the door alone to free a car unless it is genuinely urgent; a double door without its spring is a two person, high care lift, and it must never be propped and walked under.
The repair itself is measured, not guessed: the technician weighs the door and measures the broken spring's wire, coil, and length, then fits a matched pair rated for the door. Ask for the cycle rating in the quote. Standard springs run about 10,000 cycles; high cycle springs cost more now and push the next break years further out. The whole job, done right, includes a balance test you can watch: the door, disconnected, should hang halfway open without drifting.
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