A red fiber optic (LOS) light indicates a loss of signal, often caused by connection issues, incorrect setup, or ISP-related problems.

Common Causes

1. Incorrect Cable Connections: After replacing the router, the fiber optic cable may not be properly connected to the WAN/ONT port, or it may be plugged into the wrong port, preventing signal detection .
2. Loose or Damaged Fiber Cable: Bends, cuts, or damaged connectors in the fiber optic cable can disrupt the signal .
3. ISP or Service Outage: The red light may indicate a temporary outage or maintenance from your Internet Service Provider .
4. Router or ONT Configuration: A new router may require ISP-specific settings, such as PPPoE credentials, to establish a connection .
5. Power Issues: Insufficient or unstable power supply to the router can trigger a red LOS light .

Troubleshooting Steps

1. Check for ISP Outages: Visit your ISP's website or contact customer support to confirm there is no service disruption .
2. Inspect Fiber Optic Cable: Ensure the cable is securely connected, undamaged, and plugged into the correct port on the router or ONT .
3. Reboot the Router: Turn off the router, unplug it for 30–60 seconds, then power it back on. Wait for the lights to stabilize .
4. Verify Router Settings: If your ISP requires specific credentials (e.g., PPPoE username and password), ensure they are correctly entered in the new router .
5. Reset the Router: If rebooting doesn't work, perform a factory reset using the reset button. This will erase custom settings, so have your ISP credentials ready .
6. Contact Your ISP: If the red light persists after checking cables, rebooting, and resetting, your ISP may need to re-provision the connection or check for line issues .

Key Tip

Always handle fiber optic cables carefully to avoid bending or damaging them, and double-check that the new router is compatible with your ISP's fiber service. Following these steps usually resolves the red LOS light issue and restores connectivity.