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A garage door sensor that is not working stops the door going down: the opener light blinks and the door stays put or drops a little and climbs back up. Most of the time nothing is broken; the two safety beams have lost sight of each other because a lens is dusty, a bracket has been bumped or the afternoon sun is in one of them. This is how to fix a garage door sensor in the order we work through it on a driveway. If both lights are steady and the door still stops, check the other reasons a door refuses to close first.
How do garage door safety beams work?
The sensors are a pair of small boxes near the floor on each side of the opening, just inside the tracks. One sends a narrow infrared beam across the doorway and the other receives it. While the receiver sees the beam the opener may close; the moment anything breaks it, the opener stops the door and sends it back up. A beam the receiver cannot find counts the same, which is why a dirty lens or a knocked bracket behaves exactly like something in the doorway. The beams only govern closing; a door that will not open has a different problem.
What do the sensor lights mean: red, green or flashing?
Each unit carries a small light, and reading the pair tells you which side to work on. Colours vary by brand, so confirm this against the sticker on the sensor or the manual.
- One steady, one dark or flickering: the sending unit has power but the receiving unit cannot see it. Alignment, a dirty lens, glare or a damaged wire on the receiver side.
- Both dark: no power is reaching the sensors. A wire is cut or has pulled out of a terminal, or the sensor circuit in the opener has failed.
- One red, one green: on many brands this is normal, because one light means power and the other means the beam is received. Merlin's beams, for instance, generally show amber on the sender and green on the receiver, and the green one goes out when they drift.
- Flashing: a flicker on a sensor means the beam is only just getting through. A blinking motor-head light is an error code; many openers use a set number of blinks for a sensor fault, and the key is under the light cover or in the manual.
What are the five-minute fixes to try first?
Do these with the door open and the power on, so you can watch the lights change.
Five-minute sensor checks
- Wipe both lenses with a soft dry cloth. Dust, sand off the driveway and cobwebs across the lens are the most common cause we find.
- Clear the beam path. A broom against the wall, a bin, a bike wheel or a shelf that has crept forward is enough.
- Look at each bracket. If a light is dark or flickering, nudge that unit gently until it holds steady.
- Tighten the wing nut or screw while you hold the unit in line; fixings work loose after years of door vibration.
- Run your eyes along both wires up to the motor head for staples through the insulation, a crushed section or a terminal pulled out of a unit.
Test the beams after every fix
Once both lights are steady, close the door with the remote and pass a broom handle through the beam while it is moving down. It should stop and go back up at once; if it keeps coming, stop using the door until the beams are sorted.
How do you align garage door sensors?
Alignment is the fix most people need after the wipe-down. The two lenses have to point straight at each other at the same height, and the receiver's light tells you when they do.
- Find the unit with the dark or flickering light. On most brands that is the receiver and the one you adjust; leave the steady unit alone.
- Measure both units from the floor. They should match, and makers want them low, roughly ankle height; check the manual for the figure and never raise them to dodge a fault.
- Loosen the wing nut or bracket screw just enough to move the unit by hand.
- Tilt and swivel it slowly while watching its light, and stop when the light comes on and holds. A string line between the two brackets helps when you cannot get it by eye.
- Tighten the fixing and check the light again, because tightening often drags the unit a fraction out of line. A bent bracket or track leg will not hold alignment for long; straighten it.
- Close the door from the remote and do the broom-handle test.
Why does the garage door sensor stop working in sunlight?
This one is a Perth special. A garage facing west or north-west gets the low sun straight through the opening late in the day, and if it lands on the receiving lens it drowns out the infrared beam; the opener then refuses to close even though the units are clean and aligned. The giveaway is timing: the door behaves in the morning and after dark and fails between mid-afternoon and sunset.
- Shade the receiver. A short length of black conduit or a purpose-made sun hood slipped over the lens cuts the glare while letting the beam through; a cardboard tube taped on for a week proves the diagnosis first.
- Swap the two units side for side so the receiver sits where the sun never reaches; the sender does not care about glare. Some brands wire the two differently, so check the manual first.
How do you check the sensor wiring and connections?
If both lights are dark, or one flickers when nothing has moved, check the thin two-core cable that runs from each sensor back to the motor head. Unplug the opener at the power point before you touch a terminal, and keep the motor head's cover on; the mains side is an electrician's job.
- Check every terminal. Wires pull out when a bin is dragged past, and near the coast, Scarborough or Fremantle say, salt air corrodes bare copper; cut back to bright wire and refit.
- Replace old twisted-and-taped joins with a proper joiner, and mind the polarity: on some brands the two wires must land on matching terminals at the opener, or the beams will not work.
- With power restored, wiggle the cable near each unit and watch the light; a flicker means a break inside the insulation, so replace that run rather than patching it.
If everything checks out and the lights stay dark, the sensor circuit on the opener's control board may have failed, which makes it an opener repair rather than a sensor job.
How do you reset a garage door sensor after a fix?
Most sensors have nothing to reset. The opener clears the fault on its own once the receiver sees the beam again, so with both lights steady the next press of the remote should close the door. If it still refuses or keeps blinking a sensor code, run a full cycle from the wall button, then unplug the opener for about thirty seconds and plug it back in. Our guide to resetting a garage door opener and its remotes covers full opener resets brand by brand.
Why should you never bypass garage door sensors?
A garage door sensor bypass, whether bridging the wires at the opener or taping the two units together up on the motor, makes the door close on whatever is under it. The opener's force setting only reacts after the door has hit something; the beams are the one device that stops it before contact, and a child, a pet or an open car boot is what usually pays. We do not fit bypasses.
If you need the door shut tonight, use the wall button. On many openers, pressing and holding the wired wall button closes the door under constant pressure while you stand there watching it, and it stops the moment you let go; the remote will not do this, by design. Otherwise pull the manual release and lower the door by hand with someone to help.
When do garage door sensors need replacing?
Sensors last for years, but they do fail, and the signs are consistent: both lights stay dark with the cable proven good and the opener's terminals live; a lens is cracked, fogged inside or yellowed, which means moisture has got in and is common on coastal doors; or the opener keeps reporting a sensor fault after new cable, clean terminals and a careful alignment. A new pair is then the fix.
Beams are not universal. Many openers only accept their own brand's sensors, so match the pair to the opener's brand and generation. Our replacement safety beams and other opener spares are sorted by opener brand, or we repair and replace garage door sensors across Perth, same day, with no call-out fee and the price agreed before we start. We supply, install and service Merlin, Jaytech, Superlift and Steel-Line openers, our vans carry the common pairs, and we service the sensors on B&D, ATA, Gliderol and other makes too.