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Understanding the Lights on an FTTP Modem (ONT)

Last updated on by Freeola Support

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Welcome to the Freeola Help & Support pages. This guide is designed to offer an explanation of the lights seen on the most common Full-Fibre (FTTP) modems fitted by Openreach - sometimes called an ONT. For more help topics, please visit the main Support Page.

If you are a Freeola Full Fibre Broadband customer you will have an Openreach modem (or ONT) installed instead of a traditional telephone socket. This white box connects to a fibre optic cable which runs directly to your house.

There are several lights on the ONT, knowledge of what each light signifies could help diagnose faults with the service, or provide piece of mind that your connection is working as expected.

Whilst there are several different types of Openreach modem, they all work in the same way, but the type and number of lights may vary slightly between devices. Below are examples of three of the more common variations in use currently.

All images courtesy of BT Openreach.BT Openreach FTTP Modem

BT Openreach FTTP Modem

BT Openreach FTTP Modem

The table below gives a brief description of the common lights, along with details of what each means in different states.

If you are having connection issues, and have been asked to check your ONT by Freeola Support, the Actions to Take column will provide advice on recommended tests to carry out that will be useful in the fault-finding process.

Label Status Description Actions to take (if any)


The ONT has power and is turned on.  


The ONT is turned off. Check that the modem is plugged in and the electricity is on.


PON Solid Green

Fibre optic connection to the BT exchange is working.
  • If you have no internet, check the physical connection between the ONT and your router.

  • Check the configuration of your router

PON flashing / LOS off ONT is checking the connection to the exchange. Wait until light turns green, or turns off completely.
PON off, or PON and LOS both flashing Fibre optic link is not Live, or there's an issue between your property and the BT exchange.
  • Check that the white fibre optic cable is fully connected to the ONT and is not damaged.

  • Turn off the ONT for 10 minutes, then back on again. Allow up to 5 minutes for the ONT to reconnect.

PORT1-PORT4 On (any) The Ethernet connection between the ONT and your device is normal and working as expected.  
Blinking (any) Data is being transmitted between the ONT and the device connected to that port.  
Off (any) Either nothing is connected to that port, or there is an issue with the connection. Check both ends of the Ethernet cable to ensure no damage and a solid physical connection to both devices.
OPTICAL Solid Green Your line is connected.  

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