Limit switch
The setting that tells a garage door opener where the door’s fully open and fully closed positions are.
- Trolley, travelling along the rail
- Emergency release cord — red, always
- Stored open and closed limits
- Arm connecting the trolley to the door
Limit switches define travel. If the close limit is set too far, the door presses into the floor, the opener senses resistance and reverses — a fault frequently mistaken for a sensor problem. If it is set too short, the door stops with a gap at the bottom.
Older openers use mechanical screw-adjusted limits; newer ones learn the positions during a set-up routine and store them electronically.
Limit adjustment is straightforward for a technician and typically costs less than any parts-based repair, which is why it is worth ruling out before agreeing to replace anything.
Two symptoms point at limits rather than anything expensive. If the door touches the floor and then reverses back up, the close limit is set too far and the opener is reading the floor as an obstruction. If it stops with a visible gap at the bottom, the close limit is short. Either way it is adjustment work, priced well below any parts-based repair, so it is worth naming as a possibility when you describe the fault on the phone rather than accepting a quote for a new board.
Limits drift over time rather than failing outright. A chain stretches slightly, a rail settles, and a door that used to seat perfectly starts leaving a thin gap or pressing a touch too hard. That is normal wear and a normal adjustment. Worth knowing is that the limit setting is separate from the force setting: limits define where the door stops, force defines how much resistance the opener tolerates before it reverses. A door that reverses off the floor can be either, and an opener whose force has been wound up to mask a binding door is a safety problem rather than a fix — the force setting exists to protect whatever is under the door. Any adjustment to either should be followed by the reversal test: place a solid object flat on the floor in the door's path and confirm the door reverses on contact. A length of two-by-four laid flat is the traditional test object, because it sits at roughly the height at which a limb would be caught, and every opener sold in the last thirty years is required to pass it.