Step 1: Force It to Close?
Step 2: Signs to Observe
Step 3: The Sensors
The text box feature would not save when I did this Instructable, so I am overlaying colored arrows as keys to my explanation.
Most garage door problems can be traced to the sensors. The circuitry inside the sensors is quite reliable and has a long life. The first thing to check is the mounting brackets (blue arrow). Did something bend them so the sensors are no longer aligned? A quick visual inspection of each should be sufficient. In doubtful cases, you can stretch a long string between the sensors to see better if they are aligned.
The red arrow points to the LED. Each sensor has an LED. It should be bright and show a solid color. Some are green and some are red, depending on the manufacturer of your opener unit. One sensor on our unit showed a bright steady LED. The other, this one, was weak and it fluttered rapidly. That, together with the flashing ceiling light and the need to hold the switch button, are signs something is not right.
The yellow arrow points to the lens. It should be clean on both sensors. This garage is my workshop. It is always possible sawdust could have accumulated on the lenses. As a precaution, wipe them with a rag or a tissue.
The green arrow points to the wire that runs between the sensor and the opener unit on the ceiling. Look for obvious physical damage (bare wires, loose connection, cut or broken wire, etc.)
Step 4: What, Exactly, Could Be the Problem?
It has been two years since I had problems with a garage door opener, and that was a different unit than this one. I forget the procedure for troubleshooting one of these units. I have come to go on-line for help on the occasions when the garage door opener fails to work. After a quick search for "garage door opener troubleshooting," I opened this page. There are some general help pages, but they do not offer much more assistance than our manual and its suggestion to call a technician after checking a few basic things like obstructions to the infra-red beam and power to the circuit.
Help suggestions are often very brand specific. The image with this step is a chart for diagnosing problems with the sensors on a Genie garage door opener. Look closely and you can see that Genie gives diagnostic clues and codes in how many times the LEDs flash and in the color of the LED that shows something unusual. Our unit is not a Genie, but a Liftmaster. The help sections for Liftmaster units are more general and not very helpful.