Garage Door Sensor Not Working? Six Fixes to Try Before You Call

The pattern is always the same. You press the remote, the door drops a little way, then it stops, climbs back up and the light on the motor flashes at you. Nothing is broken in the door itself. The opener has simply been told, by a pair of small sensors near the floor, that something is in the way. The trick is working out what the sensors are unhappy about, and the good news is that the list of likely causes is short and most of them cost nothing to put right.

What the safety beams do

Every automatic opener sold in Australia for the last couple of decades has a pair of photo-eyes fitted low on either side of the opening, usually a hand's width above the slab. One side sends an infrared beam and the other side receives it. While the beam lands where it should, the receiver tells the motor the doorway is clear. Break the beam, even for a fraction of a second, and the opener refuses to close, or reverses if it is already moving down. It is a deliberately fussy system, because its entire purpose is to stop a door landing on a child, a pet or the bonnet of a car.

Because the sensors only guard the closing direction, a beam fault never stops the door opening. That is the quickest way to tell a sensor problem from a motor or remote problem: if the door goes up fine and only misbehaves on the way down, start here. If it will not move at all, the fault is elsewhere and the garage door won't open checklist is the better place to begin.

What the sensor lights mean

Each sensor carries a small LED, and the two lights together are your diagnostic panel. The exact colours vary by make, so check the label on the motor or the manual, but the general pattern holds across Merlin, Chamberlain, B&D, Gliderol, ATA and Steel-Line openers:

• Both lights solid: the beam is landing and the sensors are happy. If the door still reverses, look for a problem at the motor, the travel limits or the down-force setting rather than at the beams.
• One solid, one flickering or off: the receiving side is not seeing the beam. Alignment, a dirty lens or something in the path is the usual cause.
• Both lights off: no power is reaching the sensors. That points to the wiring, the terminals at the motor or, occasionally, the opener's own logic board.
• One red and one green: on many openers that is normal, since the sender and receiver use different colours. A steady red and a steady green is fine; a blinking light of either colour is the one to chase.

Six fixes to try, in order

Work down this list in order and stop when the door closes. Each step takes a minute or two and none of them needs a tool beyond a screwdriver.

1. Clear the path. Bins, a broom, a cardboard box, a child's bike or a low-hanging cobweb can all break a beam that sits only a few centimetres above the floor. Look along the line between the two sensors from one side.
2. Clean both lenses. Wipe each little glass window with a soft dry cloth, then a slightly damp one if there is a film of dust or spider residue on it. Garages collect grit, and the receiving eye only needs a thin layer to lose the beam.
3. Re-align the brackets. The sensors sit on thin metal brackets that bend if a bin or a tyre nudges them. Loosen the wing nut, aim the eye squarely at its partner, and watch the LED until it goes solid, then tighten it while holding the sensor still.
4. Check the bracket is on the track firmly. A bracket that has come loose from the track will vibrate every time the door moves and lose the beam mid-travel, which is why some doors reverse only part of the way down.
5. Look for glare. If the fault comes and goes at the same time each afternoon, sunlight is landing on the receiver. Skip ahead to the sun section below.
6. Power-cycle the opener. Switch the motor off at the wall, wait thirty seconds and switch it back on. Some boards hold a fault state until they reboot, and this clears it. If your opener needs a full reset, the guide on resetting an opener and its remotes walks through it by make.

Afternoon sun and false triggers

A photo-eye reads infrared light, and the sun puts out a great deal of it. Around Perth that matters more than in most places, because so many garages face west and the low sun in late afternoon comes straight in under a half-raised door or across a driveway and lands on the receiving lens. The receiver is flooded, it can no longer pick out its partner's beam, and the opener assumes something is blocking the doorway. Owners describe it as a door that works perfectly in the morning and refuses to close between about four and six in the afternoon in summer.

The fix is to shade the receiver rather than to fight the sun. Most sensors come with a small hood or can be turned so the sender and receiver swap sides, putting the lens that matters in the shadow of the wall. A short length of black conduit slipped over the eye, or a folded piece of card taped above it, does the same job while you wait for a proper hood. If the door reverses at dusk instead, look for a headlight from a car parked in the driveway pointing at the sensors.

Finding a wiring fault

The sensors are joined to the motor by thin two-core wire that usually runs up the track, across the ceiling and into low-voltage terminals on the back of the opener. It is a fragile run. It gets pinched by the trolley, stapled through during a renovation, chewed by rodents, or corroded where it passes the damp concrete at floor level. When both lights are dead, or one flickers no matter how carefully you align it, the wire is the next suspect.

Unplug the opener at the power point first, then trace the wire with your fingers from each sensor back toward the motor, feeling for a kink, a bare patch or a green crust at a join. At the motor, check the small screw terminals are tight and that the two wires from each sensor have not been swapped. A damaged section can be cut out and rejoined with proper connectors, but if the run is old and brittle it is often quicker to replace the whole length. Do not cut into the wire while the opener is powered, even though it is low voltage, because a short at the terminals can damage the board.

When the sensor itself has failed

A sensor that stays dark with clean lenses, straight brackets, a clear path and a sound wire has usually failed internally. Heat does it: the little black housings sit in a hot garage all summer and the electronics inside cook slowly. So does moisture. A failed sensor is not repairable and gets swapped for a new one, and this is the point where most people call us. The replacement has to match the opener, because sensors are not universal; a Merlin eye will not talk to a Gliderol board, and even within a brand the older and newer generations often differ. Our garage door sensor repair service in Perth matches the right pair to the opener, fits and aligns them and tests the door through a full cycle. We take these calls day or night, since a door stuck open is a security problem as much as a nuisance.

If the sensors look fine and light up but the door still reverses, the problem may be in the opener rather than the eyes: a worn logic board, a stuck limit switch or a down-force setting wound too low will all produce the same symptom. That is a job for our opener and motor repair side of the business, and it is worth reading the wider garage door won't close checklist first, since a bent track or a stiff spring can also make a door back up.

Why bypassing the sensors is a bad idea

Every video that shows you how to jumper the terminals or tape the sensors together facing each other is teaching you how to remove the only thing standing between a closing door and whatever is underneath it. A sectional door with its spring tension behind it will come down with real force, and the opener will not know to stop. Beyond the risk to people and pets, there is a practical problem: most modern boards detect a permanent bypass and either refuse to close or drop into a fault mode after a few cycles anyway.

The safe way to get a door closed with a faulty sensor is to hold the wall button down continuously until the door reaches the floor. Most Australian openers allow a held button to override the beams for that one movement, because a person standing there with a finger on the switch can see the doorway. Use that to lock up for the night, then fix or replace the sensor properly the next day. There is no call-out fee and the job is priced before any work starts, so you know where you stand before we fit anything.

The sensor wiring and alignment diagram for your model is in the opener manual, which the Merlin support centre hosts for its range, and Product Safety Australia lists recalls on powered doors and openers.