Won't Close: Check Photo Eye vs Force vs Track First, Sequencing Tree

Why this matters

A door that will not close, or that starts down and reverses, has three common and very different causes: a blocked or misaligned photo-eye safety sensor, a force or travel-limit setting that is fighting the door, or a mechanical track problem adding resistance. Checking them out of order wastes time and can mask a safety fault. The photo eye is checked first for a reason: it is the federally mandated entrapment-protection device, it is the most common cause, and a tech who reaches for the force adjustment first risks dialing out the very protection that is doing its job. Sequencing keeps the diagnosis fast and keeps the safety system intact.

Symptom presentation

• Door reverses immediately on the close command and the opener lights blink: classic photo-eye fault.
• Door closes most of the way then reverses near the floor: force or travel-limit, or an obstruction near the floor.
• Door closes with a button held in constant-pressure mode but reverses in normal mode: confirms the entrapment sensor is triggering.
• Door binds, jerks, or labors on the way down: track, roller, or alignment resistance read by the force sensor.

Quick checks

1. Check the photo eyes first. Inspect both sensor LEDs: a steady indicator on both means aligned and clear; a blinking or dark indicator means blocked, misaligned, or miswired. Clear obstructions, wipe lenses, and realign until both read steady.
2. Inspect the close path for obstructions near the floor: a trash can, a rope, ice, or a raised section of weatherstrip catching.
3. Watch the door travel down and feel for binding. A door that labors mechanically is feeding resistance to the force sensor.
4. Only after eyes and obstructions are clear, evaluate the force and travel-limit settings.

Isolation tree

Branch 1, immediate reverse on close, sensor LED blinking or dark. Photo-eye fault. Causes: misalignment, a dirty or sun-flooded lens, a loose or damaged wire, a bumped bracket. Realign so both LEDs are steady, clean the lenses, repair the wiring. Confirm a normal close.

Branch 2, eyes steady and clear, door still reverses partway down. Move to mechanical resistance. Watch the door descend. Binding, a hesitation, or a noise points at a track, roller, or alignment fault adding load that trips the force sensor. Correct the mechanical issue (bent track, dry or seized roller, debris in track, door slightly off-track) before touching force.

Branch 3, eyes clear, travel smooth, door still reverses just above the floor. Now the travel-limit or close-force setting is the suspect. A down-limit set too short makes the opener think the door hit something. Close force set too low reverses on normal seal compression. Adjust the down limit to the true floor position and set the close force to the minimum that closes the door reliably, then verify the door still reverses on a 1.5-inch obstruction.

Branch 4, closes in constant-pressure mode only. This confirms the entrapment system (eyes or force) is intercepting in normal mode. Do not leave the customer in constant-pressure mode; find and fix the triggering cause from branches 1 to 3.

A common field trap is the sun-flooded photo eye. A low morning or evening sun shining directly into the receiver lens overwhelms the sensor's signal and reads as blocked, so the door reverses only at certain times of day and works fine otherwise. The customer reports an intermittent "won't close" that you cannot reproduce at midday. Shade or reposition the receiver, or swap the sender and receiver sides so the receiver faces away from the sun. This is a real photo-eye fault, not a force or track problem, and it stays in branch 1 even though the symptom is intermittent.

Wiring at the eyes deserves a closer look than most techs give it. A staple driven through the low-voltage sensor wire, a corroded splice, or reversed polarity all produce a steady-reverse or a flickering LED. Run the sensor wire by hand looking for pinches and staples, and confirm the wire colors land on the correct opener terminals. A sensor that has good lenses and good alignment but a damaged wire will fail exactly like a misaligned eye.

Confirming diagnosis

The order is the diagnosis. Steady eye LEDs clear the sensor. A smooth manual and powered descent clears the track. A door that then closes on minimum force and still reverses on a test obstruction confirms the force and limits are set correctly and safely. Never confirm a fix by raising force past the point where the door still reverses on a placed obstruction, because that is the entrapment test that must pass.

Remediation

• Photo eye: realign brackets to steady LEDs, clean or shade lenses, repair or replace wiring and sensors.
• Obstruction: clear the close path, reset weatherstrip, remove debris.
• Track and rollers: straighten track, replace seized rollers, reseat a door drifting off-track.
• Force and limits: set the down limit to the floor, set close force to the reliable minimum, then verify the 1.5-inch obstruction reversal.

End by running the door through a full cycle and confirming reversal on a test obstruction laid on the floor.

References

• UL 325, Standard for Door, Drape, Gate, Louver, and Window Operators and Systems, entrapment-protection and reversal requirements.
• ANSI/DASMA 102, Specifications for Sectional Doors, operational criteria.
• DASMA Technical Data Sheet 353, Photoelectric Sensor and Reversing System Guidance.