Short answer: when a garage door starts to close and then goes back up, or will not close at all, the cause is most often the two safety sensors near the floor. They are blocked, dirty, out of line, or have a loose wire. That is something you can check yourself in a couple of minutes. If the sensors are fine, the next most likely causes are the opener's travel settings, something binding in the tracks, or a broken spring or cable, and those last two need a technician.
Check the Safety Sensors First
Every opener made since 1993 has a pair of photo-eye sensors, one on each side of the door opening, four to six inches above the floor. One sends an invisible beam and the other receives it. If the beam is broken while the door is closing, the door reverses. If the opener cannot see the beam at all, it refuses to close.
- Look at the lights. Each sensor has a small light. On most openers both should be steady. A light that is off, dim or blinking means the sensors are not seeing each other.
- Clear the path. A broom handle, a bin, a leaf or a cobweb in front of a sensor is enough.
- Wipe the lenses with a soft, dry cloth.
- Check the aim. Sensors get knocked by bikes, bins and feet. Loosen the wing nut, point the sensor at its partner until the light goes steady, and tighten it again.
- Look at the wires. Follow the thin wire from each sensor. A staple through the wire, a chewed section or a wire pulled out of its terminal will stop the door closing.
- Consider the sun. Low sun shining straight into the receiving sensor can blind it for part of the day. If the problem happens at the same time each day, that is the likely reason.
Many openers also tell you directly: the main light flashes a set number of times, or the wall button blinks, when the sensors are the problem. Your opener's manual lists the codes.
Match the Symptom to the Cause
| What the door does | Likely cause | What to do |
|---|---|---|
| Starts down, then reverses; opener light flashes | Safety sensors blocked or misaligned | Work through the sensor checks above |
| Reaches the floor, then goes straight back up | Close-travel or force setting is off, or the floor is uneven or iced | Clear the threshold; if it continues, the opener needs adjusting. See opener repair |
| Stops partway and reverses, always in the same place | Something binding: a bent track, worn roller or debris | Look for an obvious obstruction. Do not force it. See garage door repair |
| Remote does nothing but the wall button works | Remote battery, or the wall control's lock (vacation) mode is on | Replace the battery; turn the lock feature off at the wall control |
| Nothing responds at all | No power to the opener | Check the outlet, the breaker and any GFCI outlet in the garage |
| Door closes crooked, or one side hangs lower | A lift cable has slipped or snapped | Stop using the door. See cable repair |
| Door slams down, or is suddenly very heavy | Broken spring | Stop using the door. See spring replacement |
Other Common Causes
- Travel and force settings. The opener is set to stop at a certain point and to reverse if it meets resistance. If those settings drift, the opener can decide the floor is an obstruction. Adjustment is done at the opener and differs by model; if you are not comfortable with it, it is a quick job for a technician.
- Ice, snow and swollen thresholds. In winter a ridge of ice or packed snow under the door is enough to trigger a reversal. Clear the threshold completely.
- Tracks and rollers. A dented track, a seized roller or a loose track bracket makes the door bind on the way down. You may hear it grind or see it shudder at one spot.
- The manual release has been pulled. If the red cord was pulled, the opener runs but the door does not move. Re-engage it by running the opener until the trolley reconnects, or follow your manual.
- Worn opener parts. A failing circuit board or a worn gear can cause erratic behaviour that no setting will cure.
How to Get the Door Closed Tonight
If the sensors are the problem and you need the door shut, many openers will close the door while the wall button is pressed and held for the whole of its travel; releasing the button makes the door go back up. Check your opener's manual to confirm that yours works this way. If you use it:
- stand at the wall control where you can see the whole doorway;
- make sure nothing and nobody is in the door's path, and keep children and pets out of the garage;
- keep watching until the door is fully closed.
Holding the button means the sensors are not protecting anyone, so treat it as a way to secure the house once, not a way to keep using the door. Have the sensors repaired before the door goes back into normal use.
Do not use the override, and do not pull the red release cord, if the door is crooked, a cable is loose, or you suspect a broken spring. A door in that state can drop.
When to Stop and Call
- The door is crooked, off its track, or a cable is hanging loose.
- You heard a loud bang and the door is now very heavy.
- The door closes far too fast or slams.
- You have checked the sensors and the door still reverses.
- The door is stuck open and you cannot secure the house. See emergency garage door repair.
Never try to adjust or repair springs, cables, the drums at the ends of the spring bar, or the brackets at the bottom corners of the door. They are under enough tension to cause serious injury.
Related Guides
- Garage door won't open? What to check first
- Garage door stuck open: what to do
- Garage door safety features explained
Frequently Asked Questions
Door still won't close?
Tell us what it does when you press the button and we will take it from there.
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