Almost every door that lifts happily and then refuses to go down is not broken in the way people assume. The opener has been told that closing would be unsafe, and it is doing exactly what federal rules require of it. Work through the causes in order of likelihood and the answer often turns up in five minutes without a tool in your hand.
1. The Photo Eyes Have Lost Each Other
UL 325 has required entrapment protection on residential openers since 1993. In practice that means a matched pair of photo eyes, one on each side of the opening, mounted four to six inches above the slab and aimed at each other. One lens sends an infrared beam, the other watches for it. Break that beam and the door will not travel down, full stop. Most units also blink the opener light or an LED on the sending eye to tell you which fault they are seeing.
Look at those two indicator lights before you look at anything else. Steady on both generally means the pair is talking. Dim, flickering or dead on one means the beam is missing its target, or the low-voltage wire behind it has been damaged. Nudge it, do not wrench it. The bracket is soft steel and light thumb pressure will sweep the aim through alignment while you watch the light go solid.
Alignment does not only drift because a bike handlebar caught it. Irving sits on expansive clay that swells and shrinks with the seasons, and slabs move with it. When the floor and the surrounding block move a fraction of an inch, the brackets bolted to each vertical track move too, so a pair that was dead-on in the spring can be a degree off by August.
2. A Fogged, Filmed or Sun-Blinded Lens
The eyes can be aimed perfectly and still fail. A film of dust bound up with old lubricant overspray, a spider web strung between the lens and the jamb, or dew sitting on cold plastic on a humid morning all scatter enough infrared to break the signal. West-facing garages add a stranger version of the same problem: low afternoon sun striking the receiving lens head-on can wash out the beam it is trying to detect, which is why some doors only misbehave between six and eight in the evening.
Wipe both lenses with a dry soft cloth. Skip glass cleaner and any solvent, because those craze the plastic and leave you with a permanently hazy eye. If sunlight is the trigger, the long-term fix is a small shade or a repositioned bracket rather than repeated cleaning.
3. The Close Limit Is Set Too Deep
Your opener does not know where the floor is. It knows how far to travel before it should consider the door shut, and that figure lives in a limit setting on the motor head. Set it slightly too far and the door reaches the slab, keeps pushing, feels the resistance, decides it has hit a child or a bumper, and reverses. The tell is timing: the door touches down and bounces straight back up rather than stopping short in mid-air.
Limits and force are adjusted together and in the right order, which is why this one is usually worth handing over. Dialing force upward to overpower a limit that is wrong is how a healthy opener destroys its own drive gear.
4. Real Resistance in the Down Direction
Sometimes the opener is right and there genuinely is something fighting it. A flat-spotted roller that skids instead of turning, a hinge that has cracked at the barrel, a vertical track pinched inward at one point, or a torsion spring that has weakened enough to unbalance the door all create a hard spot the motor reads as an obstruction.
Pull the emergency release cord with the door closed, then lift by hand. A properly balanced door moves with light effort at every point and stays roughly where you leave it around waist height. If you can feel a spot where it drags, or it wants to run away from you, the fault is in the door hardware and no opener setting will paper over it. That is the point where roller replacement, hinge and bracket work, or spring service is the actual repair.
5. A Locked Wall Console or a Latched Vacation Switch
Most wall consoles carry a lock button, sometimes labeled vacation mode. Held down for a couple of seconds it disables every remote and keypad while the wall button keeps working, which produces the odd symptom of a door that answers the button on the wall and ignores everything else. Children lean on it. So do stacked storage boxes. A short press usually clears it, and the console light stops blinking when it does.
6. Something Physical Under the Door
This is the least glamorous cause and it still accounts for real calls. Check the threshold along its whole width, not just the middle:
- A pebble, screw or hardened lump of mud sitting in the seal channel
- Leaf litter and grass clippings packed into the corner behind the jamb stop
- A trash bin, hose reel or trailer jack parked inside the beam line
- A bottom seal that has torn loose and is folding under itself as the door lands
When to Stop Guessing and Call
Clean the lenses, check the indicator lights, clear the threshold and test the lock button. Those four are safe for anyone. Stop there if the door lifts unevenly, if you can see a gap in a torsion spring above the door, if a cable has gone slack, or if the opener strains and groans on the way down. Photo-eye and sensor work is inexpensive, and honest diagnosis of the rest costs you a phone call. Describe exactly what the lights are doing when you ring, because that single detail decides which parts come off the truck.