A garage door opener should reverse when the door meets an obstruction while closing. Checking that is a reasonable task for a homeowner, and it takes only a few minutes. What you need to decide is how far to go. Some checks are simple enough to do yourself. Others involve parts that should only be handled by a trained technician.
What the reversal test checks
The common check is to place a solid object, such as a short length of wood, flat on the floor where the door will meet it, then press the close button and watch what happens. The door should stop and reverse when it touches the object. Make sure no one is standing under the door during the test, and keep your hands and feet clear of the track. Repeat the check if the door has a separate photo-eye sensor, and confirm the sensor lights are aligned and unobstructed.
What you can check and adjust yourself
Clean the sensor lenses and check that the sensor brackets have not moved. Confirm the wiring to the sensors is intact and not pinched. Look at the force or limit adjustment screws on the opener if the manual describes them, and adjust only as the manual directs. Keep the track clean and free of debris. These tasks fall within what a homeowner can reasonably do with the manual in hand.
What belongs with a technician
Do not adjust the door springs or the tension of the cables yourself. Spring work carries serious risk and is a job for a trained technician with the right tools. If the door fails the reversal test after you have cleaned and aligned the sensors, if the opener strains or stops mid-travel, or if the door shows damaged track or worn rollers, book a service visit. Ask the technician to run the full safety check and to record the results.
How to decide
Ask yourself three questions. Can I complete the test and the sensor check using only the manual? Am I comfortable making the adjustment the manual describes? Does the problem involve springs, cables, or the drive mechanism? If the answer to the first two is yes and the third is no, the task is yours. If the third is yes, book the visit. If the door keeps failing the test after your adjustments, stop and call a technician rather than adjusting further.
Keep a record
Note what you checked, what you adjusted, and what the door did. The same notes will help a technician if you do book a visit. The planning figures for openers are on the garage door opener guide, which lists the typical service life and when to plan a replacement.