Internet & modems

Fiber ONT has no lights at all

An ONT with no lights at all is a power problem rather than a signal problem, and checking the power adapter, outlet, and any backup battery is the first step before assuming the unit has failed.

Difficulty
Easy
Time
10–15 minutes
DIY cost
$0
Pro cost
$0

Symptoms

  • No lights are lit on the ONT, including the power light
  • ONT was working before and stopped after a power outage
  • Power adapter feels warm or makes no sound/vibration when plugged in
  • Backup battery indicator (if equipped) shows a warning

Likely causes

  • CommonPower adapter unplugged or outlet not workingThe most basic explanation for no lights at all is that the unit isn't receiving power.
  • CommonBackup battery depleted after a power outage (if the ONT has one)Some ONTs include a battery backup for phone service continuity during outages, and a depleted battery combined with no wall power leaves it fully off.
  • PossibleFailed power adapterPower adapters fail independently of the device they power more often than people expect.
  • Less commonONT hardware failureAfter ruling out power, the unit itself may have failed internally.

What to do

  1. Confirm the power adapter is plugged into both the ONT and a working wall outlet, testing the outlet with another device if possible.
  2. If the ONT has a battery backup compartment, check whether it's included and whether its low-battery indicator is lit; if power was recently restored after an outage, allow time for it to power up normally.
  3. Try a different outlet, ideally not on a switched circuit or a power strip that might be off.
  4. If you have a spare power adapter with matching voltage and polarity, test it to rule out a failed original adapter.
  5. Wait several minutes after restoring power, since ONTs can take a bit longer than typical routers to fully power up and sync.
  6. If no lights appear on a confirmed working outlet with a known-good power adapter, contact your provider, since the unit itself is provider-owned equipment in most fiber setups and can be swapped by them.
  7. Do not attempt to open or repair the ONT yourself, since it's typically leased or owned by the provider.

When to call a pro

Since the ONT is usually provider-owned equipment, contact them directly for a replacement if power troubleshooting doesn't bring any lights on.

Safety

Generally low risk

Generally low risk for a careful person. Stop if anything looks different from what this guide describes.

Related guides

Operator provides AI-generated troubleshooting information. It can be wrong. For safety-critical, electrical, gas, structural, medical, automotive safety, or other high-risk problems, consult a qualified professional.