Garage door troubleshooting library
Updated . Every manufacturer code and safety rule on this page links to its source below.
Short answer
Start from what the door is doing, not from a guess about the part. Most opener problems trace back to the safety sensors, the travel limits, or a door that is binding or out of balance. These guides paraphrase the opener makers' own charts (LiftMaster/Chamberlain, Genie, Linear) and the door industry's safety data sheets from DASMA, with every source linked. Anything involving springs or cables goes to a trained technician.
- Garage door opener blink codes by brandLiftMaster/Chamberlain, Genie and Linear flash codes, paraphrased from each manufacturer's own chart.
- Garage door won't close: step-by-step diagnosisSafety sensors, lock mode, limits and the door itself, in the order to check them.
- Garage door closes then reversesWhat it means when the door goes back up right away, mid-travel or at the floor.
- Torsion spring sizing explainedWire size, inside diameter, length, wind and DASMA color codes, and why springs are a pro-only job.
Find your symptom
| Symptom | Go to |
|---|---|
| Opener light or arrows blinking a pattern | Blink codes by brand |
| Door will not close, lights flash | Won't close |
| Remote does nothing, wall button works | Lock or vacation mode |
| Door goes down, then back up | Closes then reverses |
| Door opens, then drifts down | Closes then reverses (drift section) |
| Loud bang, door suddenly heavy | Torsion springs |
| Grinding, squealing, popping | Garage door sounds |
| Door hangs crooked or a cable is loose | Spring vs cable |
Before you touch anything
Safety first
- Find the opener's model number on the label on the side or back of the motor unit. Chamberlain says it is the key to the right code chart, and the same is true for every brand.
- Keep everyone out of the doorway while the door moves. Linear's manual says never to go under a stopped, partly open door.
- DASMA says springs, cables and their brackets are under high tension and must only be repaired or adjusted by a trained door systems technician. If a spring is broken, do not run the door.
The two monthly safety tests
DASMA encourages homeowners to test the door's safety systems every month:
- Photo-eye test. Start the door closing, then pass an object through the beam near the floor. The door should reverse and return to fully open.
- Reversal test. Lay a 2x4 flat on the floor under the center of the door (DASMA notes it is 1½ inches tall that way) and close the door. It should reverse when it touches the board.
DASMA says photo-eye beams must sit no higher than 6 inches above the floor so a small child cannot crawl under them. If either test fails, stop using the opener and have it serviced.
Frequently asked questions
How often should I test my garage door's safety features?
Monthly. DASMA describes monthly testing of the reversing mechanism with a 2x4 laid flat under the door, and of the photoelectric sensors by breaking the beam while the door closes. In both tests the door must reverse.
Does every garage door opener have to have safety sensors?
Federal rules require entrapment protection on residential garage door operators manufactured on or after January 1, 1993 for sale in the United States. DASMA explains this means inherent force sensing plus a secondary device such as photoelectric sensors or an edge sensor that meets UL 325. DASMA's checklist says an opener without these protections should be replaced.
Do garage door openers in California need a battery backup?
Yes. DASMA notes that, under a California law, all residential garage door operators sold or installed in California after July 1, 2019 must have battery backup functionality.
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Sources
Codes and rules are paraphrased from these documents. Charts vary by model and software version, so your owner's manual wins if it disagrees with this page.
- TDS-364, Installation Location of Photoelectric Sensors on Residential Garage Doors, DASMA, as of 2026.
- TDS-369, FAQ Regarding Automated Residential Garage Door Systems, DASMA, as of 2026 (rev. 2020).
- TDS-167, Residential Sectional Garage Door and Electric Operator Checklist, DASMA, as of 2026 (rev. 2023).
- 16 CFR 1211.1, Effective date (Safety Standard for Automatic Residential Garage Door Operators), U.S. Code of Federal Regulations (via Cornell LII), as of 2026.
- Linear LDCO850 Homeowner's Manual, Important Safety Instructions, Nortek Security & Control (Linear), as of 2026.
- Diagnostic codes for garage door openers (finding your model and chart), Chamberlain Group support, as of 2026.
More homeowner guides: garage door safety, when to replace an opener, repair cost ranges, and the Top Rated pros by city.