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Troubleshooting an Openreach ONT fibre modem
Troubleshooting an Openreach ONT fibre modem
Updated over 8 months ago

This article covers:

  • What the lights mean and which lights should be on when the device is working properly

  • Steps to work through before contacting the Care Team

Light status

When working properly, the items in bold for each light below indicates a good connection/service.

Power (Checking the power from the mains)

  • Solid green: Powering or has powered up

    • Move on to PON light status

  • Flashing green: Updating the firmware

    • The device should be back online within 5-10 minutes

  • Red: Boot up has failed

    • Reboot the ONT by removing the power cable or pressing the reset switch for less than 5 seconds

    • If that fails, using a paperclip or similar, hold the reset switch for 10-15 seconds to perform a factory reset of the ONT

    • If the fault continues, contact the Care Team

  • Off: No power

    • Check that the power cable has no visible signs of damage and is securely in place

    • Try the power adapter in another socket

      • If the device works in another socket, we suggest you get an electrician to check the socket

    • Check that there is power in the property (try the lights or turn on an appliance that doesn't have a battery back up source)

PON (The ONT connection from your local exchange to the network)

  • Solid green: When the ONT has established a connection to the local exchange

  • Flashing Green: It's establishing a connection

    • The device should be back online within 5-10 minutes

  • Off: Can't detect the optical cable

    • Check the green fibre optic cable is connected to the ONT properly. Be very careful handling the cable as the fibre is delicate and can be damaged if not handled carefully.

    • Reboot the ONT by removing the power cable or pressing the reset switch for less than 5 seconds

    • If that fails, using a paperclip or similar, hold the reset switch for 10-15 seconds to perform a factory reset of the ONT

    • If the fault continues, contact the Care Team

LOS (Connection status to the external network)

  • Off: The connection is working as expected

  • Red: There's a problem with incoming connection

    • Reboot the ONT by removing the power cable or pressing the reset switch for less than 5 seconds

    • If that fails, using a paperclip or similar, hold the reset switch for 10-15 seconds to perform a factory reset of the ONT

    • If the fault continues, contact the Care Team

Data (The connection status between the ONT and the router)

  • Green: The ONT has connected to your router

  • Flashing Green: The ONT is passing data to and from the Internet

  • Off: The ONT and router aren't connected

    • Check the Ethernet cable is connected to both the ONT's Ethernet port and the router's Internet port

    • Ensure that the router is powered on

    • Ask the customer if they can swap the Ethernet cable for a new/different one to rule out a faulty cable.

    • If the router is powered off and will not power on, proceed to the Which router do I have? article

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