A surprising number of opener complaints are solved without any parts. These checks are all safe to make yourself.
The door closes then reverses
Nine times out of ten the photo-eye sensors near the floor are misaligned or dirty. Wipe the lenses and check that both indicator lights are steady rather than blinking. A leaf, a bike wheel or a bin can also break the beam.
Remotes work only up close
Usually a flat battery, occasionally interference from an LED bulb in the opener head. Swap batteries first.
The motor runs but the door does not move
The drive gear or carriage has probably failed. Plastic shavings on the floor under the motor confirm it. This one needs a technician.
It worked fine until a recent repair
Travel and force limits need re-setting after a door's balance changes. That adjustment should be part of any spring or cable job — if it was skipped, the opener will behave oddly.
When to stop and call
If the door is out of balance, the opener will keep failing no matter how many parts you throw at it. Have the door tested by hand before replacing a motor.