Most guides to a garage door that won't seat start and end with the photo-eye sensors, and for good reason: dirty or misaligned eyes cause the majority of these calls.

Few garage-door quirks are as maddening as one that closes almost all the way, pauses, then rolls back up on its own like it changed its mind.

You press the button, the door does nothing, and you sit in the driveway wondering what just broke.

It is a bad morning. You need to leave; the car is sitting in the garage, and the door will not move.

Look up at the torsion spring above a garage door and the rust is usually the first thing that catches the eye: a dusting of orange along coils that used to be a uniform gray. It's tempting to file that color next to the rust on a porch railing, annoying but not urgent.

A garage door spring looks like something you could pick up at a hardware store: a coil of steel, the same basic shape as the spring in a screen door or a pen. That resemblance is exactly what gets people hurt. A garage door spring isn't a bigger version of a hardware-store part.

If you have ever looked up at your garage door and wondered what exactly is holding all that weight, the answer comes down to one of two spring designs. Both do the same basic job: they counterbalance the door so the opener (or you, by hand) does not have to lift its full weight every time it opens.

You go to raise the door, and it lurches up crooked, one side lagging behind the other. Down the wall, a thin steel cable that should be taut is hanging slack, or worse, coiled in a loose nest on the garage floor.

One corner of the door is riding lower than the other. There is a wedge of daylight where the door should meet the frame, a roller dangling off its rail, and the whole thing looks like it is leaning against the opening instead of hanging in it.

Your garage door has started reversing partway through its closing cycle, or hesitating right before it seats on the floor, and nothing about it has obviously changed. Nobody adjusted the opener. Nobody touched a dial. The springs look the same as they always have, and the track isn't visibly bent, yet the door isn't finishing the way it used to. The force setting is almost always the answer, even though no one laid a hand on it.

The gate has worked fine for months. Then a week of gray, drizzly weather rolls through, and it starts crawling through its swing, hesitating before it starts, or not opening at all. Nothing about the gate changed. What changed is upstream, in a panel and battery box most people never think about until the gate stops cooperating.

The sections come off the truck crated face down, cardboard between them, and somebody reaches for one end to slide it clear.

Your door is hanging crooked, a roller has left its rail, and you are standing there wondering if you can just run it a couple more times to get the car out. The honest answer is no.

A spring replacement call spends its opening stretch on everything except the spring. A tape measure comes out.

The opener sounds exactly like it always does. The motor whirs, the light clicks on, the chain or belt slides along the rail, and the door sits there. Or it crawls up a few inches, groans, and gives up.

A garage door starts creaking on the way up, and the sound seems to come from the spring above the opening.

Stand off to one side of the opening, press the button, and watch the steel bar spanning the header.

It usually happens on an ordinary morning. You hit the wall button on your way out. There is a bang from the garage, like someone dropped a bowling ball on concrete, and the door lurches and stops. Now the opener hums, the door sits there, and your car is stuck behind it.

A gust catches the gate mid-swing, and for a second everything about it changes: the panel takes the wind full in the face, and the hinge-side post absorbs a shove it wasn't necessarily built for. That moment loads the hinges and post in a way ordinary opening and closing never does, and it's why a gate that sits solid and level when closed can still develop a lean, a twist, or a slam problem once the wind starts working on it.

Most people picture the choice between a swing gate and a slide gate as a style question: a swing gate reads as traditional; a slide gate reads as more modern. Looks matter less than most people assume, though.