Photo eyes & sensors

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.

How do I confirm the photo eyes are the problem?

Hold the wall button down continuously. If the door closes while you hold it and refuses to close any other way, the photo eyes are the fault and the opener is fine — most openers allow a constant-pressure close specifically so you can make that distinction.

Then read the indicator lights. Under 16 CFR 1211.10(a)(5) any alignment-dependent sensor must carry a means of showing proper alignment, which is what those small LEDs are. A steady light on both units usually means they are seeing each other. A flickering, dim or dark light on the receiving side usually means they are not. Which colour means which varies by manufacturer, so check the sticker on the bracket rather than a general rule.

Three causes account for most of it: a lens filmed over with dust or a cobweb, a bracket knocked out of line by a bike or a bin, and late afternoon sun landing directly in the receiving eye. All three are free to rule out and take under five minutes.

If the lights are steady and clean and the door still will not close, stop looking at the sensors. Watch when it reverses: a door that reverses after touching the floor is usually a travel limit, not a beam.

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.