Photo eyes and safety sensors
A blocked or misaligned photo eye is the most common reason a garage door will not close. Federal rules require the sensors to stop the opener closing an open door when the beam is broken, so a dirty lens does not just interrupt the door — it prevents closing entirely. Realigning takes minutes.
Why a blocked beam stops the door completely
This is the part almost nobody explains. Under 16 CFR 1211.8(a)(1), a secondary entrapment protection device must do three things when it activates: reverse a closing door, return it to the fully open position, and prevent the operator from closing an open door.
That third requirement is why your door will not budge downward. It is not a fault. The opener is refusing to close because federal rules require it to refuse while it believes something is in the opening.
Reading the indicator lights
16 CFR 1211.10(a)(5) requires any alignment-dependent sensor — a photo eye is the obvious case — to be “provided with a means, such as a visual indicator, to show proper alignment and operation.” That is what the small LEDs are for, and it means your door is legally required to be able to tell you what is wrong.
Broadly: a steady light means the pair is seeing each other, and a flickering, dim or dark light means it is not. Which colour means which varies by manufacturer, so check the sticker on the bracket or your manual rather than trusting a general rule.
The four-minute fix
- Look at both sensors, mounted 4 to 6 inches above the floor per CPSC guidance.
- Wipe both lenses with a dry cloth. Cobwebs and road film are the single most common cause.
- Clear the opening — a bin, a bike wheel, a coiled hose, a snow bank.
- If a light is still flickering, loosen the wing nut on the bracket, tilt the sensor slowly until the light goes steady, and retighten without moving it.
- Check for low direct sun on the receiving eye. Late afternoon sun can swamp the receiver; a small shade or a sun-blocking sleeve fixes it.
Never bypass them
You will find advice to twist the sensor wires together or tape the eyes facing each other to force the door shut. That removes the external entrapment protection required since 1993, and it is the exact protection that exists because about 73 children have been killed under closing garage doors since March 1982. If the sensors are genuinely faulty, replace them — they are among the cheapest parts on the door.
When it is not the sensors
If the door closes when you hold the wall button down continuously, the sensors are the fault, not the opener: most openers allow a constant-pressure close specifically to distinguish this. If the door reverses after touching the floor instead of before, the travel limit is the more likely cause. If the door reverses partway down with clean, aligned sensors, look for an obstruction in the track.
How does a garage door actually hold its own weight?
A garage door is not lifted by the opener. It is lifted by the spring, and the opener only guides it. That distinction explains almost everything else on this page.
A residential door weighs between 85 and 400 pounds depending on size and material. The counterbalance system — springs, cables, drums and bottom brackets — stores the energy needed to raise that weight and gives it back on the way up. With the counterbalance set correctly the door stays put when released halfway, and the opener only has to overcome friction.
This is why an unbalanced door destroys openers: the motor ends up lifting a load it was never sized for. And it is why springs and cables are professional work while sensors and remotes are not — one group holds that stored energy and the other does not.
The test is available to anyone. Disconnect the opener with the red release, lift the door halfway by hand, and let go. If it stays where you left it, the counterbalance is right. If it drifts down or shoots up, it is not, and CPSC says a door in that state should be serviced by a professional.
What order should I check things in?
Cheapest and safest first, because that order also happens to be the most likely. Start with the remote battery, then the wall button, then whether the opener has power at the outlet — a tripped GFCI accounts for more "dead openers" than any component failure.
Next check the photo eyes, because a blocked beam does not merely interrupt one cycle. Federal rules require secondary entrapment protection to prevent the opener closing an open door at all while the beam is broken, so a filmed-over lens presents as a completely dead door in the closing direction.
Only then test the door itself. Pull the red release with the door closed and lift by hand. If it moves freely, you have an opener or control problem. If it is very heavy, you have a counterbalance problem, and that is where the DIY path ends.
The federally required text in your own manual draws the same line: it directs cable and spring repairs to a qualified service person, and it says never to go under a stopped, partially open door.
What does federal law actually require here?
More than most people assume, and in writing. Every residential opener manufactured on or after January 1, 1993 for US sale must meet 16 CFR 1211, which incorporates the entrapment protection provisions of UL 325.
Three concrete requirements matter to a homeowner. A downward-moving door must begin reversing within 2 seconds of hitting an obstruction and return to the fully open position. There must be a second, independent protection system — a photo eye, an edge sensor, or an equivalent device — which must also prevent the opener closing an open door. And the manual release handle must be red, reachable at 6 feet, and release under no more than 50 pounds of pull.
The part almost nobody cites is §1211.16(b), which specifies the exact words the manufacturer must print in your manual. Among them: “Have a qualified service person make repairs to cables, spring assemblies and other hardware.” That is why this page's verdict on springs and cables is not our opinion.
What UL 325 and 16 CFR 1211 require covers the full standard.
What is the one-minute test everyone should be doing?
The reversal test, monthly. This is not our advice — it is the text federal law requires the manufacturer to print in your opener's manual.
“Test door opener monthly. The garage door MUST reverse on contact with a 1½ inch object (or a 2 by 4 board laid flat) on the floor.”
Lay it flat on the floor in the door's path and close the door. It must reverse on contact. If it does not, stop using the opener until it is adjusted per the manual, repaired, or replaced.
It matters because this system fails silently. A door whose reversal has stopped working looks and sounds exactly like one that still does, right up until something is underneath it. CPSC reports about 73 children aged 2 to 14 trapped and killed under automatic garage doors since March 1982 — roughly 3 a year — and that record is why the standard exists.
CPSC also recommends inspecting the door and opener every 30 days. Children, pets and the garage door covers the rest.
At what point should I stop and call someone?
There are four signals, and any one of them on its own is enough to stop.
- The door is very heavy by hand with the opener disconnected. The counterbalance has failed, and nothing but you is holding the door.
- You can see a gap in the spring coil, or a cable that is frayed, slack, or off its drum.
- The door sits crooked, higher on one side, or has come off its track. It is still under full tension and can move suddenly.
- The door does not reverse on the board test. The entrapment protection is not working.
None of those is calling too early. They are precisely the cases where the federally required manual text directs the work to a qualified service person, and where the cost of being wrong is not a broken part.
The rule worth teaching at home comes from that same federal text, in capitals: “NEVER GO UNDER A STOPPED PARTIALLY OPEN DOOR.”
Questions that come up next
Does a door that reverses mean something is broken?
No — the opposite. A door that stops and goes back up when it touches something is the entrapment protection doing exactly what 16 CFR 1211 requires. The fault worth investigating is a door that fails to reverse.
Can I disable the photo eyes to get the door closed?
No. That removes the external entrapment protection required since 1993, and it is the protection that exists because of the CPSC child fatality record. If a sensor is genuinely faulty, replace it — it is among the cheapest parts on the door.
Is it safe to use the emergency release with the door open?
The federally required manual text says to use it only when the door is closed wherever possible, because weak or broken springs may allow the door to fall rapidly. A great deal of DIY content advises the opposite.
Should I replace one spring or both?
If the door has two, quote both. The second is the same age and has taken the same number of cycles, so it is next. This is one of the few upsells in the trade that is genuinely honest.
Sources
- Publication 523 — Non-Reversing Automatic Garage Door Openers Are a Hazard — US Consumer Product Safety CommissionTier 1 accessed
- 16 CFR Part 1211 — Safety Standard for Automatic Residential Garage Door Operators — US Consumer Product Safety CommissionTier 1 accessed