Garage Door Closes Then Immediately Reopens
A garage door that closes and immediately reopens is the opener detecting what it believes is an obstruction. The usual causes are the down travel limit set too far, so the door presses into the floor, misaligned photo eye sensors, or a down force setting that is too low for the door.
What the opener is thinking
Modern openers have two independent ways of deciding something is in the way.
The photo eyes watch an infrared beam across the opening. Break it and the door reverses.
The force monitor watches how hard the motor is working. If the door meets more resistance than the setting allows, the opener assumes it hit something and reverses.
A door that reverses at the very bottom of its travel is almost always the second one, and the reason is usually the travel limit rather than a real obstruction.
Cause one: the down travel limit
The limit tells the opener where the floor is. If it is set slightly too far, the opener drives the door into the slab, meets resistance, and reads that as an obstruction.
The tell is that it happens every time, at exactly the same point, with the door fully closed.
The fix is adjusting the down limit on the opener, usually a dial or a button sequence depending on the brand. It is part of any tune-up.
Cause two: the photo eyes
Check both indicator lights. Steady on both means aligned.
Look for a bracket that has been knocked, a cobweb across a lens, a wire that has been caught or chewed, or low direct sunlight into the receiving lens.
If the fault is intermittent, or time of day dependent, this is where to look.
Cause three: down force set too low
Less common, and usually the result of somebody adjusting it after a different problem.
Before turning it up, check the door is not actually harder to move than it should be. Pull the manual release and run the door by hand through its full travel. If it binds anywhere, the resistance is real and turning up the force just means the opener forces through it.
The one thing not to do
Do not solve this by turning the force up until the door stays down.
That setting is the only thing stopping the door from crushing whatever is under it. An opener with the force wound up is a genuine hazard, and a door that reverses is telling you something rather than misbehaving.
Related questions
Why does it only happen sometimes?
Intermittent reversal usually points at sensors rather than limits. Sunlight, a swinging cobweb, or a loose bracket that moves when the door runs will all produce a fault that comes and goes.
Can I just turn the force up?
You can, and it is often the wrong fix. Turning the force up tells the opener to push harder against whatever it meets, including a person. Find out why it is meeting resistance first.