It opens perfectly. You press the button to close it, it comes down two feet, stops, goes back up, and the light on the opener blinks at you. Do it again and the same thing happens.
This is the single most common garage door call there is, and it is very often something a homeowner can fix in five minutes without any parts. It is worth knowing how, because it is also a call that can be talked into a new opener.
What the two little boxes do
Near the bottom of each vertical track, four to six inches off the floor, is a small plastic housing. One transmits an infrared beam across the opening, the other receives it. If the beam is interrupted while the door is closing, the opener stops and reverses.
Openers have been required to have this kind of protection since the early nineties, and it is the reason a modern garage door does not close on a child or a pet. If your opener has no sensors at the bottom of the tracks, that is not a vintage machine that needs troubleshooting, that is an opener to replace.
The important detail: the opener will not close on the wall button or the remote if the beam is not confirmed. It will open, because opening is not the dangerous direction. That asymmetry is the fingerprint of a sensor problem, and it is how you tell this apart from every other fault.
The lights are the diagnosis
Both sensors have an indicator LED, and reading them takes ten seconds.
On most units, the sending unit’s light is on steadily whenever it has power. The receiving unit’s light is on steadily when it is seeing the beam, and it flickers, dims or goes out when alignment is lost.
So: if the receiving light is out or flickering, it is an alignment or obstruction problem. If both lights are out entirely, it is power or wiring. If both are steady and the door still will not close, the problem is somewhere else and you can stop looking at sensors.
The exact behaviour differs slightly by manufacturer, and there is a label on the motor head telling you which is which.
The five causes, in order
1. Something is in the beam. Obvious, and worth doing first because it costs nothing. The beam is only a few inches off the floor and crosses the whole opening. A bag, a bin, a garden hose, a box that has slumped sideways. Look along the floor line, not at eye level.
2. A sensor has been knocked. They are mounted on light brackets in the most kickable location in the garage. A bicycle handlebar or a mop is enough. Loosen the wing nut, aim it at the other one, and tighten it when the receiving light goes steady. Take your time: they are more directional than they look.
3. Sun on the receiver. This is the one nobody guesses, and it produces the most maddening version of the fault: the door will not close in the late afternoon and is perfectly fine in the morning. Low sun shining directly into the receiving sensor saturates it so it cannot pick out the beam. West-facing garages in this metro get this every autumn and spring. The fix is a shield, or simply swapping the sending and receiving units so the receiver faces away from the sun.
4. Dust, spiders and condensation on the lenses. A soft dry cloth. Spiders in particular seem to like the warm housing, and a web across a lens attenuates the beam enough to cause intermittent faults rather than clean ones.
5. The wiring. The sensor wire runs along the floor line and up the track, which is the most abused wire in the building. Look for staples driven through the insulation, crushed sections, breaks where somebody moved a shelf, and corrosion at the terminals on the motor head. Water on the garage floor gets into low connections and produces faults that come and go for weeks.
When it is not the sensors
If both lights are steady and the door still reverses, three other things do this.
The close force setting is too low, so the opener interprets normal friction as an obstruction. Do not simply turn it up: ask why the door needs more force than it used to, because that is a door problem and turning the force up disables the protection.
The travel limit is set too far, so the door reaches the floor before the opener thinks it should, hits it, and reads that as an obstruction. This one reverses at the very bottom rather than partway down.
The door is binding at a point in its travel because of a track, a roller or a hinge. Pull the release and move it by hand: you will feel it.
The money question
No prices, and for once the reason is that four of the five causes have no parts at all. Alignment, cleaning, moving an obstruction and shading a sensor are free, and we would rather talk somebody through them on the phone than take the call-out.
Where there is a cost: a replacement pair of sensors is a small part. A wiring run is labour. A logic board, if the sensor circuit on it has failed, is the expensive end and is the point at which the age of the opener becomes the real question.
What not to buy
- Do not buy an opener because the door will not close. Check the two lights at ankle height first. It is the most oversold call in this trade.
- Do not buy a bypass. People do this. Holding the wall button down to force a close is a documented override for a genuine emergency, and wiring the sensors out permanently removes the only thing stopping the door closing on someone.
- Do not buy sensors before checking the wire. A broken conductor gives exactly the same symptom as a dead sensor and new sensors will not fix it.
- Do not turn the force setting up to get past it. That is not a fix, it is the removal of a safety system.
The short version
Look at the two small lights near the floor. Steady means aligned. Out or flickering means alignment, dirt, sun or wire, and all four of those are things you can sort out yourself before anybody comes out.
We do get a bit of grief for publishing that. It is still the honest answer, and it saves everybody an afternoon.
Garage Doors Pro Service · (469) 693-9000 · garagedoorsproservice.com
Serving Dallas, Plano, Frisco, McKinney and the DFW metro.
