A door that stops a few inches off the floor, leaving a strip of daylight under the bottom seal, usually has its down travel limit set short. If it nearly lands and crawls back, look at close force or the safety eyes.
People keep hitting the remote. Or they yank the emergency release and try to shove it down by hand. That is how you stretch a cable, crush a roller, or teach the opener a travel limit that is wrong for the door you actually have.
This is different from a door that starts closing then climbs right back up. That one usually reverses from halfway, or kisses the floor and pops back up. This one gets close, then quits or crawls back a little. Same opener, different place in the cycle, often different hardware.
If it hangs with a clean gap all the way across
Most often the down travel limit is set short. The opener thinks it has arrived before the seal does. The motor stops humming. The door sits there with a neat strip of light under it. The photo eyes may look fine.
Travel limits are model specific. Some openers use labeled screws on the head. Others use a learn button and arrow keys. Read the sticker on your unit before you twist anything. Tiny increases only. The door should gently meet the floor and compress the seal. It should not strain or bounce.
If you are not sure which screw or button is which, stop. Leave it for a shop.
If it almost lands then crawls back a little
Different story. The door gets within a couple inches, then reverses like it hit something. A close force setting that is too light can treat a sticky roller, a stiff seal, or grit near the sill as an obstacle. Dirty or crooked sensor lights can also refuse the last bit of travel even when nothing is in the path.
Wipe both lenses. Check that both LEDs look the way the sticker says they should when they are aligned. Do not tape over the eyes. Do not crank the force dial to max so it will smash through whatever is binding. That defeats the safety reverse.
If one side seals and the other side does not
Look at the bottom seal and the threshold. A worn or torn weather strip can hang on one corner. A warped bottom panel can leave daylight on the high side while the low side already touches. Debris in the track, a bent rail end, ice along the sill, or a ridge in the concrete can stop one edge first.
Pull the emergency release only if the door still feels balanced by hand. Lower it slow from the side. If one corner scrapes or the door lists hard, leave it. That is track, cable, or panel work, not a limit tweak.
If a new weather seal or ice created the gap
A thicker bottom seal can steal the last half inch. Wet seal stuck to cold concrete can stall the last inch while the panel stays even. Warm the sill. Do not pry from under the panel. That is different from a door stuck halfway.
When the last inches feel heavy
A tired or broken spring can make the final stretch feel like dead weight even though the door still moves most of the way. The opener may quit early to protect itself. If the door feels much heavier by hand than it used to, or you heard a bang earlier in the week, do not keep mashing the button. Do not climb a ladder to wind cones.
What it is not
Not a roller out mid opening, and not a silent remote. Here the motor runs and the door almost lands.
What not to do
Do not climb under a hanging door to finish the close with your shoulder. Do not tape over the eyes or spin travel screws in big jumps while the door moves. If you need the garage sealed for the night, lower it by hand only when it still feels balanced, then leave the opener disconnected until a shop checks limits, sensors, seal, and spring balance.
I am not a contractor. This is just what shows up when a door almost closes and people keep mashing the button. A shop that does garage doors will check travel and force settings, clean and aim the eyes, look at the bottom seal and tracks, and rebalance.
Safety notes on openers and reverse live on DASMA's garage door opener page.
The U.S. CPSC garage door operator page covers federal rules for automatic openers.
If yours stops short and you want someone local to look, get a quote.