First do not try to lift the door by hand or using the opener as you can hurt yourself lifting a heavy garage door by hand and burn out the opener using it to try to open a door with a broken spring.
Broken torsion spring garage door.
You will have to look up at the springs to determine if one is broken.
Just like car tires are rated by miles garage door springs are rated by an estimated number of cycles 1 cycle your garage door going up and down one time.
If you have a wayne dalton torquemaster system pictured below the springs will be inside a tube.
This video will show you how to open a garage door if one of the torsion spring is broken.
If your garage door has two torsion springs the second spring will keep the cables tight and on the drums.
A garage door that has a broken spring has nothing to support its weight.
The springs used by our competition range anywhere from 5 000 10 000 cycles whereas we use a high grade steel spring rated for 25 000 50 000 cycles.
Replacing garage door springs is not a do it yourself project replacement requires special tools and techniques to prevent injury.