Broadband Hardware

What do the lights on my OpenReach Full Fibre modem mean?

lights openreach full fibre modem

Congratulations! If you’re reading this then I’m guessing you’ve upgraded to Full Fibre, or FTTP (Fibre to the Premises) as it’s also known. With vastly superior speeds over traditional fibre broadband, it’s slowly rolling out across the UK.

One aspect of the installation is a wall mounted modem (known as an ONT – Optical Network Terminal), which goes between the fibre connection outside and your router. No matter which ISP you’re with, OpenReach will have installed this for you and it will be one of their branded boxes.

They’ve gone through a number of different models but, right now, are installing a compact little box made by Nokia. This is what it should look like…

lights OpenReach Full Fibre modem

Yes, this is mine.

Underneath the box, from left to right, are 3 connectors – power, LAN out, optical fibre in, That middle one is the one that goes to your router.

As you can see there are 4 lights at the top of the OpenReach Full Fibre modem – Power, LOS (Loss of Service or Loss of Signal), PON (Passive Optical Network) and LAN (Local Area Network – but you know this one, right?). Think of LOS as showing a cut in the fibre connection, whereas PON is indicating your connection at the other end of the network.

Here’s what those lights really mean…

LightStateWhat it means
PowerOnThe ONT has power
PowerOffThere is no power to the ONT. Check the power cable is properly in (the one on the left-hand side) and that the mains connection on the other end is switched on.
LOSOffYou have a working fibre connection
LOSOnYou have a fibre connection issue – check the fibre connection in the bottom of the ONT.
PONOffNo network connection has been made.
PONOnYou have a working network connection.
PONFlashingThe ONT is negotiating a connection on the network. You’ll find this might happen a few times after initial installation.
LANOffThere is no data transmitter to your router – check the LAN cable!
LANFlashingThe shows that data is transmitting successfully to your router

So, a full working connection should look like this…

PowerOn solidly
PONOn solidly

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About the author

David Artiss

Works for Automattic Inc., the company behind and Tumblr. Tech geek, international speaker and occasional PC Pro podcaster. Lover of Lego and video games.


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  • Thanks. Very helpful. How does this coexist with a BT telephone socket ? Currently the small wall box (Master Socket 5C) has two connection points – one for the VDSL and the other for the phone.

  • My new box has fell off the wall how do I redux it as I can’t open the box to Re-screw it

  • Hello David, I think that you need to change the order in which you have listed the connection on the bottom of the Nokia ONT when viewed from the front. You have written:

    “Underneath the box, from left to right, are 3 connectors – power, optical fibre in, LAN out. That last one is what goes to your router.”

    Which I think should read as:

    “Underneath the box, from left to right, are 3 connectors – power, LAN out (this one goes to your router), optical fibre in.”