A garage door that will not close is a different kind of problem from one that will not open. It is not a heavy-lifting failure, it is a communication failure: something is telling the opener not to complete the movement, and the job is working out what.
The good news is that it is usually inexpensive. The bad news is that it is the fault most often misdiagnosed as a dying opener, and a replacement opener costs several times what the actual repair does.
First, identify which of three behaviors you have
These look similar and mean entirely different things, so be precise:
- The door starts down and reverses almost immediately. The safety beam is being broken. Start with the safety sensors.
- The door goes all the way down, touches the floor, then rides back up. The beam is fine. The problem is at the bottom of the travel.
- The door stops partway and just sits there without reversing. Different fault again, usually the opener meeting a load it will not push through.
Getting that distinction right on the phone narrows the diagnosis enormously before anybody sets off, and it decides what goes on the truck.
Cause one: the photo eyes
The pair of sensors a few inches above the slab send an infrared beam across the opening. Break it and the door reverses. This is not a manufacturer nicety: under federal rule, openers built on or after 1 January 1993 must carry a second independent layer of entrapment protection, and photo eyes are how nearly every unit provides it.
Safe things you can check yourself: look at the indicator lights, because on most makes both should be steady and one that is out, flickering or a different color points at that side. Wipe both lenses with a soft dry cloth. Check nothing has knocked a bracket out of aim, which a bike or a recycling bin does routinely.
Cause two: the coastal one
Here is the version specific to Carlsbad, and it is the one that catches people. The door closes perfectly for a week, then refuses twice in a day, with no pattern anyone can identify. Nothing has been knocked. The lenses are clean.
That intermittency is the signature of corrosion at the terminals where the thin sensor wires screw into the photo eye bodies, or at a staple partway along the run. Corroded terminals give inconsistent contact rather than clean failure, and inconsistent contact produces exactly this maddening behavior.
Look for green powder or discolouration at those terminals. It is often visible without tools. Cleaning and reterminating resolves it, and a sensor pair is an estimated $105 to $215 if the sensors themselves have gone. Both of those are far below a replacement opener at an estimated $445 to $795, which is why the diagnosis is worth more than the parts on this fault.
Cause three: the bottom seal
If the door travels all the way down, makes contact and then reverses, the photo eyes are almost certainly innocent. What is happening is that the door meets real resistance at the last inch and the opener reads that as an obstruction, which is precisely what it is designed to do.
The usual culprit is a bottom seal that has hardened with age and lost its flex. Instead of compressing softly against the slab it pushes back. Squeeze the rubber: if it feels stiff and does not spring back, that is likely your answer. A new seal and stops is an estimated $135 to $275.
On this coastline there is a second version worth checking. If the bottom rail of the door has corroded and distorted, it may no longer meet the slab evenly, which produces the same symptom for a different reason and needs a different fix.
Cause four: the travel limit
Openers store the positions of fully open and fully closed. If the down limit is set slightly past the slab, the opener drives the door into the floor, reads the resistance, and reverses. Limits drift after a power interruption, and they must be reset after any work that changes how the door moves, which includes every spring or cable replacement.
This one is genuinely a settings job rather than a parts job, and it sits in the settings band at an estimated $85 to $215 along with realignment and a lens clean.
The thing never to do
Do not solve this by raising the sensors, taping over one, or holding the wall button down as a permanent arrangement.
The mounting height exists so the beam catches a small child or a pet. The Consumer Product Safety Commission wrote the entrapment rules after a long history of children being trapped under closing doors, and it asks homeowners to test the reversal every month. If the sensors are being fouled at the correct height, the answer is to fix whatever is fouling them, not to defeat the safeguard.
How to test that it is working properly
Two separate tests, checking two separate systems:
- Photo eyes: with the door closing, break the beam with an object, not your hand. The door should stop and reverse immediately.
- Force reversal: lay a flat board on the slab in the door's path and close the door onto it. It should reverse on contact.
A door that fails the second test is a genuine hazard and should not be used until it is corrected. Any competent visit ends with both of those proved, because the force settings the second test depends on are calibrated to a balanced door, and any work on the counterbalance invalidates them.
Short version
- Reverses immediately: photo eyes. Reverses after touching the floor: seal or limit.
- Intermittent with no pattern, near the coast: corroded sensor terminals. Look for green powder.
- Almost none of these justify a new opener.
- Never raise, tape over or bypass a sensor.
- Test the reversal monthly, on a flat board.