Guided check
0/3 checkedMatch the symptom, then work through the safe checks.
1. What best matches what you observe?
2. Complete only the checks that are safe for you.
Contact the fiber providerOptical power and line faults require provider testing.Professional
3 user-level checks are available in this guide.Stop immediately if any warning condition applies.
Show stop conditions
- The fiber connector would need to be unplugged or cleaned
- The cable is crushed, cut, or sharply kinked
Likely causes
- The provider fiber signal is absent
- The fiber cable is sharply bent, disconnected, or damaged
- A connector is contaminated or disturbed
- The ONT or provider equipment has failed
Quick checks, in order
Do not look into or touch the fiber end
Fiber light can be invisible and connectors are easily contaminated.
Check only visible cable routing
Look for a loose external connector or sharp bend without unplugging it.
Restart the ONT only if the provider permits
Wait for the full optical registration sequence.
Contact the fiber provider
Optical power and line faults require provider testing.
Which optical lights are on?
LOS red and PON off
The ONT is not receiving or registering optical service.
LOS flashes intermittently
The signal may be marginal or the fiber path unstable.
PON is normal but internet is down
The optical link may be fine; router, account, or service routing is next.
Stop and get qualified help when
Do not continue troubleshooting if any of these apply:
- The fiber connector would need to be unplugged or cleaned
- The cable is crushed, cut, or sharply kinked
Frequently asked questions
What does LOS stand for?
It commonly means Loss Of Signal.
Can rebooting fix red LOS?
It may recover a temporary ONT state, but it cannot repair a missing or weak optical signal.
Did this guide move you closer to a solution?The response is stored on this device and sent to aggregate analytics.