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Near the floor on each side of the garage opening sit two small garage door sensors — often called safety beams — firing an invisible infrared beam at each other. Their one job is proving the doorway is empty before the opener lets a heavy door come down. When that proof fails for any reason, the door won't close, reverses back up, and the opener light usually blinks. So "my garage door won't close" is usually a seeing problem rather than a door problem, and most seeing problems cost nothing to fix.
How garage door safety beams work
One unit sends, the other receives. Break the beam while the door is closing — a bin, a bike wheel, the dog — and the opener stops and reverses straight away. The system is built to fail safe: if the receiver can't see the sender for any reason (dirt, misalignment, a dead unit, a cut wire), the opener treats the doorway as blocked and won't close under power. That's why sensor faults leave a door stuck open rather than closing blind — annoying on purpose, and far better than the alternative.
How to fix a garage door sensor, step by step
- Clear the beam path — bins, brooms, hoses and boxes stacked by the opening are the most common cause
- Wipe both lenses with a soft, dry cloth — dust, cobwebs and salt film build up over months
- Read the lights: both steady means healthy, one blinking or off means misalignment, both dark means power or wiring
- Turn the knocked sensor gently by hand until its light goes from blinking to steady
- Tighten the bracket so it can't drift again, then close the door with the remote to test
- Finish with the timber test: close the door onto a piece of timber laid flat — it must touch and reverse
Need the car out right now?
On most openers, holding the wall button down the whole way will close the door while you watch the doorway yourself. That's the legitimate workaround while a sensor fault waits for repair — taping the sensors together is not.
How to reset garage door sensors
There's no reset button on the sensors themselves, and usually no separate one for them on the opener. The nearest thing is a power cycle: switch the opener off at the power point for 30 seconds, switch it back on, and let it check the beams again as it starts up. That clears a control board that got confused after a storm or outage. If the lights are still blinking afterwards, the problem is alignment, dirt or wiring, not a stuck setting. The opener reset guide covers the power cycle and the other resets in full.
Won't close in the afternoon? It's the sun
Here's the one that confuses everyone: a door that closes perfectly all morning and refuses later in the day. That's low afternoon sun, sometimes bounced off a light-coloured driveway or wall, flooding the receiving sensor until it can't pick its partner's beam out of the glare. West-facing garages with an open outlook get it most. The fix is a small shade over the receiving sensor, moving it slightly, or swapping the sending and receiving units so the receiver faces away from the sun. No amount of lens cleaning cures it.
Wiring faults: the intermittent kind
The sensors talk to the opener through thin low-voltage wire run along the wall at skirting height — where it gets nicked by trailers and mowers, chewed by rodents, perished by sun, or pinched by the staple holding it. A dark light on one sensor while the other is lit usually means broken wire rather than a dead unit. Wiring is also behind the maddening version where the sensors work for days and then drop out when something moves the loose strand. If your fault comes and goes, suspect the wire before the sensors.
How to tell if a garage door sensor is bad
- Cleaning and realignment fix it for only a day or two at a time
- A sensor light stays dark even though the wiring checks out
- The housings are sun-bleached, cracked or brittle
- The opener still reports a blocked beam with the doorway clear and the lights steady
Garage door sensors often last a decade or more, less where salty, humid air gets into the electronics. Replacements must match the opener's brand, which is why a random online pair so often won't work. Our garage door sensor repair replaces, rewires or realigns the pair and always finishes with a real auto-reverse test. The price is confirmed before any work starts. For the door-won't-close symptom more broadly, the garage door won't close checklist covers the non-sensor causes too.
Why you never bypass them
There are videos showing how to tape the sensors together so the opener always sees a clear beam. Understand what that does: it permanently blinds the only system watching for a child, a pet or a car boot under a closing door that weighs more than a fridge. Sensor faults are among the smallest genuine repairs a garage door needs — there's no version of the maths where defeating the safety system wins. Having the beams checked and the auto-reverse tested is part of every regular garage door service.
