A door that feels heavy when you lift it by hand, even with the opener disengaged, usually means the spring has already lost most of its tension - it just hasn't broken yet. A door that won't budge, with a visible gap in the coil above the door, means it has broken. You may also hear a sharp crack from the garage sometime when no one's touching the door at all; that's a spring letting go on its own.
On the newer builds typical of this area, we also see cable fraying where it rides the drum, usually a few years after the spring itself starts to weaken, since a tired spring puts more load on the cable than it was sized for. If your opener is straining, reversing, or the door creeps down after you open it, check the spring before you call about the motor.