Fiber ONT shows a red light

Symptoms

• ONT's power light is on but another light (often labeled LOS or PON) is red
• No internet on any device connected to the ONT or router
• Light was previously green and changed to red without any known cause
• Fiber cable at the ONT looks intact but the light is still red

Likely causes

• CommonDamage or a break in the fiber optic line, often outside the homeFiber lines can be damaged by construction, weather, or wildlife along the path from the street to your home.
• CommonProvider-side equipment issue at the local distribution pointA problem at the neighborhood fiber hub can cause a loss-of-signal light in every home it serves.
• PossibleFiber cable disconnected or improperly seated at the ONTThe delicate fiber connector can come loose, though it should generally not be handled without care.
• Less commonONT hardware failureAfter ruling out the line itself, the ONT unit can fail internally.

What to do

1. Check that the ONT has power and the power light is on and normal.
2. Look at the fiber cable connection where it enters the ONT; if it appears loose, you can gently ensure it's seated, but avoid bending, unplugging, or touching the actual fiber connector end, since it's fragile and sensitive to dust.
3. Restart the ONT by unplugging its power for 30 seconds and plugging it back in, then wait several minutes for it to attempt to resync.
4. Check your provider's outage map or call support, since a red LOS light is very commonly caused by an issue on their network or the outside fiber line.
5. Avoid attempting to repair, clean, or reconnect the fiber optic cable itself, since it requires specialized tools and improper handling can damage it further.
6. Report the specific red light (mention 'LOS' if that's the label) to your provider, since it tells them precisely what kind of issue to look for.
7. Expect that a red LOS light almost always requires a technician visit to resolve, since it typically indicates a break or fault in the physical fiber line.

When to call a pro

A red LOS light on a fiber ONT almost always requires your internet provider to send a technician to inspect and repair the fiber line, typically at no cost if the fault is on their side.

Safety