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

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…

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…

So, a full working connection should look like this…

What to do if your Full Fibre connection isn’t working

If the lights on your ONT aren’t showing the expected pattern (Power on, LOS off, PON on, LAN flashing), here’s a quick troubleshooting checklist you can try before calling your ISP:

1. Check the power
   Confirm the ONT’s power cable is firmly connected at both ends and that the plug socket is switched on.
2. Inspect the fibre cable
   The fibre optic cable is delicate — check that it’s not bent sharply, pinched, or dislodged from the ONT.
3. Reboot your ONT and router
   Turn off both devices at the wall, wait 30 seconds, and turn them back on. Wait a few minutes for the PON light to stabilise.
4. Test with a new Ethernet cable
   A faulty LAN cable can stop data from reaching your router. Try swapping it out if you’re getting a LAN light issue.
5. Contact your ISP
   If the LOS light stays on or PON won’t stop flashing after rebooting, contact your internet provider. It could indicate a network issue further up the line.

Can you move your OpenReach ONT to a different room?

A common question after installation is whether the ONT can be moved elsewhere in the house. The short answer is not easily. The fibre cable is usually installed through a drilled hole in the external wall and runs directly to the ONT’s position.

If you really need to relocate it:

• You’ll need a qualified fibre engineer to move the internal fibre extension and reinstall the ONT.
• Some ISPs offer this service for a fee (often £100–£150 depending on the complexity).

If your issue is poor Wi-Fi signal, a more practical alternative is to keep the ONT where it is and use mesh Wi-Fi systems or a high-speed Ethernet cable run to your preferred router location.

Can you connect multiple devices to the ONT?

Most OpenReach Full Fibre ONTs only have one active LAN port. If you want to connect additional devices (like a second router, NAS, or PC directly), you’ll need to:

• Plug a network switch into the LAN port of your router, not the ONT.
• Or check if your ISP supports multi-port ONTs (rare in the UK residential market).

Directly plugging devices into the ONT is typically unsupported, as it bypasses your router’s firewall and DHCP functions.

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This article was updated on the 23rd June 2025