The garage door motor runs, but the door does not move

What you are hearing

You press the remote. The motor hums, the light comes on, the chain or belt on the rail may even move — and the door stays exactly where it is. It is the single most common garage door fault in Cape Town, and it is also, in most cases, the cheapest one, which is why it matters not to be sold a new motor for it.

A garage door motor has two halves: an electric motor that turns, and a drive that turns that rotation into a pull on the door. When you can hear the first half and the second half is doing nothing, something between them has given way. There are three usual suspects, and a technician can tell them apart at the door in a few minutes.

The three usual causes

The first is the drive gear. Most domestic motors turn the rail through a plastic or nylon gear, and after some years — sooner on a heavy or unbalanced door — its teeth strip. The motor spins, the gear spins with it, and nothing engages. You often hear a faster, freer whirr than usual, and there is sometimes a scatter of white plastic dust under the motor housing. This is a gear kit, fitted in under an hour, and a motor repair rather than a replacement.

The second is the trolley. The carriage that rides along the rail and is connected to the door by the arm has a release — the red cord — and if it has been pulled, or its catch has worn, the motor drives the rail while the trolley sits still. If you or anyone in the house pulled the cord during a power cut and never re-engaged it, that is the answer, and the fix is to run the motor until the trolley clicks back in. If the catch has worn, it is a trolley.

The third is the door itself. A motor is not designed to lift a door; it is designed to move a door that its springs have already made weightless. If a spring has snapped or lost its wind, the door weighs sixty or eighty kilograms again, and the motor's force limit stops it before it strains — so it hums, tries, and gives up. On a sectional, look at the torsion spring above the door for a visible gap. On a tip-up, try the manual release and lift: if the door is heavy, the motor was never the problem.

What to check before you call

Pull the red release cord and lift the door by hand. If it moves easily and stays where you leave it, the door is balanced and the fault is in the motor or the trolley — a small job. If it is heavy, or slams down, or will only stay at the top, the spring is the fault and the motor should not be run again until it is fixed.

Look at the rail. If the chain or belt is moving and the trolley is not, it is the trolley or the release. If nothing on the rail moves while the motor hums, it is the gear.

Do not force the door, and do not keep pressing the remote: a motor driving against a stalled load for minutes is how a cheap gear fault becomes a burnt motor.

What the repair involves, and what it costs

A gear kit is the cheapest common repair on a garage door — the part is modest and the labour is under an hour. A trolley is similar. A spring is more, because the part is heavier and the job is not one to do without the right tools, but it is still far less than a new motor. The honest cost ranges are in a separate guide.

A technician who quotes a new motor for a door that hums without opening, without first pulling the release and lifting the door by hand, has not diagnosed anything. The right first question is whether the door is balanced; everything else follows from the answer.

When the motor really is finished

Sometimes it is. A motor that hums and smells hot, a board with visibly corroded tracks on the Atlantic Seaboard, a unit whose parts are no longer made, or a developer-grade motor on a double door it was never rated for — on those, a gear kit is a repair to something that was never right, and a motor sized for the door is the honest answer. The diagnosis at the door says which, before any work starts.