A solid green PON light with LOS off is the normal optical state on an Openreach full-fibre (FTTP) connection. A flashing or unlit PON, a red LOS light, or an ONT with no lights indicates a connection, power or network problem. Start with power and Ethernet checks, then restart the ONT for 30 seconds and use its reset button for 10–15 seconds only if the problem remains. Your broadband provider—not Openreach directly—owns the support case and must escalate faults. On the agreed activation date, Openreach says service should be live before midnight.
What the Openreach ONT lights mean
The wall-mounted Openreach box is the optical network terminal (ONT). It converts the fibre signal into an Ethernet connection for your broadband provider’s router. Read the lights before changing anything: the combination of PON, LOS, LAN and power indicators usually identifies which part of the connection needs attention.
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| Light state | What it usually means | What to do |
|---|---|---|
| Solid green PON; LOS off | The optical connection is working normally. | Check the Ethernet link, router and devices if you still have no internet. Ask the provider to test the service if those checks pass. |
| Flashing PON | A possible connection or optical-network problem. | Complete the power and cable checks. If it keeps flashing, report the exact state to the provider. |
| PON off | May indicate a network issue. | Check power first, then contact the provider if PON does not return. |
| Red LOS | Loss of service or an optical fault. | Do not open or repair the fibre. Contact the provider for diagnosis and escalation. |
| No lights | The ONT may have no power, or the unit may have failed. | Check the mains supply and report it to the provider if the power light cannot be restored. |
| Solid PON and LAN | Openreach’s setup video describes this combination as connected and ready to go. | If browsing still fails, investigate the router, authentication, Wi‑Fi or device rather than the fibre light itself. |
The PON indicator describes the optical-network side; it does not prove that your router has internet access. Conversely, a normal PON with no browsing can mean a loose Ethernet plug, an incorrectly configured router or a service that has not yet been provisioned.
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- ONT: the wall-mounted Openreach unit connected to the incoming fibre.
- Router: supplied or specified by your broadband provider; its WAN, Internet or FTTP port connects to the ONT.
- Activation date: the date agreed with the provider. Openreach says the Full Fibre service should be activated before midnight on that date.
Most installations take between one and four hours, according to an Openreach installation statement; that is an installation estimate, not a guarantee that every order will be live immediately. Keep the ONT and router on a mains socket and avoid moving or repeatedly unplugging the wall-mounted unit.
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Step-by-step Openreach FTTP troubleshooting
1. Check mains power to both boxes
- Confirm that the ONT’s power supply is plugged into a working mains socket.
- Confirm that the router is also switched on and connected to mains power.
- Check for a tripped switch or a loose power adaptor connection, without moving the fibre connection itself.
- Observe the ONT again. If it has no power light after the socket and adaptor checks, tell the broadband provider; an engineer may be required.
Openreach advises powering the wall-mounted unit and router from a main socket and avoiding unnecessary unplugging. Do not disconnect the optical fibre or open the ONT enclosure.
2. Read and record every ONT light
Write down whether power is on, whether PON is solid, flashing or off, whether LOS is red or off, and whether LAN is lit. The provider can use that information to distinguish a local cable or router problem from an optical fault. A single description such as “the internet is down” is less useful than “PON is flashing, LOS is red and LAN is off.”
A solid green PON with LOS off is the normal optical state. If that is what you see, proceed to the Ethernet and router checks rather than trying to repair the fibre. A persistent flashing PON, an off PON or a red LOS should be treated as a provider-support issue after the basic power check.
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3. Reseat the ONT-to-router Ethernet cable
- Find the Ethernet lead running from the ONT’s LAN socket to the router’s WAN, Internet or FTTP socket. Use the port named in your provider’s instructions; router labels vary.
- Unplug and firmly reconnect both ends until each plug clicks into place.
- Inspect the lead for cuts, crushed sections or bent connectors.
- If available, try a known-good replacement Ethernet cable. A spare FTTP router cable is useful when the original is damaged, loose or missing, but it cannot fix a red LOS or persistent flashing PON.
- Check whether the router’s WAN or Internet indicator changes after reconnection.
The cable must connect the ONT to the router—not to an ordinary numbered LAN port unless the provider specifically instructs that arrangement. If you are unsure which router socket is the WAN/FTTP port, use the provider’s model-specific instructions rather than guessing.
4. Test the router and your devices separately
- Try at least two devices, such as a phone and a laptop.
- If possible, connect one computer to the router by Ethernet to avoid confusing a Wi‑Fi problem with a fibre fault.
- If only one device fails, restart or reconnect that device; the broadband line may be healthy.
- If every device fails but PON is solid and LOS is off, ask the provider to check router configuration, authentication and service provisioning.
- Where possible, try another compatible router. If the second router works, the original router is the likely fault.
Do not interpret a phone’s inability to join Wi‑Fi as proof that the Openreach fibre is down. The ONT can be operating correctly while the router’s wireless network, password, configuration or firmware is the actual problem.
5. Restart the ONT in the documented order
- Turn the ONT off at its power source.
- Wait a full 30 seconds.
- Turn it back on and allow the lights time to settle.
- Check PON, LOS and LAN again, then test the router and a device.
A restart can clear a temporary state, but it will not repair a cut or disconnected optical path. If the same flashing PON, red LOS or no-light condition remains, continue to the documented reset step and then contact the provider.
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6. Use the ONT reset button only after the restart
- Locate the small reset button or pinhole on the ONT.
- Use a paper clip or SIM-eject tool to press it for 10–15 seconds, until the lights go out.
- Release the button and wait for the unit to power up and complete its light sequence.
- Recheck the Ethernet connection and test more than one device.
If the fault continues after the reset, stop repeating it and contact the broadband provider. The reset is a documented troubleshooting action; it is not a substitute for optical repair or provider-side service testing.
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“Why is my Openreach PON light flashing?”
Openreach’s self-install guidance treats a flashing PON as a possible connection issue. First verify mains power, reseat the ONT-to-router Ethernet lead, restart the ONT for 30 seconds and perform the 10–15-second reset if necessary. If PON still flashes, report that exact state to the provider. Do not open the fibre path or attempt to clean, splice or reconnect the optical cable yourself.
“What does a red LOS light mean?”
LOS means loss of service in the optical connection. A red LOS is therefore not a normal router or Wi‑Fi symptom. Check that the ONT has power, but do not bend, remove, clean or repair the fibre. Tell the provider that LOS is red and provide the PON and LAN states; the provider can run line tests and escalate to Openreach.
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“Why do I have no internet when PON is solid?”
A solid PON with LOS off says the optical side is normal, not that every part of the broadband service is configured. Reseat the Ethernet lead, verify the provider-designated WAN/FTTP port, test a second device and try a wired connection. If all devices fail, the provider should check the router’s configuration, authentication and provisioning. If another compatible router works, focus support on the original router.
“Why are there no lights on the ONT?”
No lights usually points first to power. Check the mains socket, power adaptor and switch. If the ONT remains dark, report it rather than repeatedly unplugging or moving it. An engineer may be needed, particularly when the router also has no WAN link.
“The LAN light is off—does that mean the fibre is broken?”
Not necessarily. LAN reflects the Ethernet link between the ONT and router. A disconnected, damaged or incorrectly placed cable can leave LAN off while the optical PON remains normal. Reseat both ends and try another known-good Ethernet cable. A solid PON and LAN combination is described in Openreach’s setup transcript as connected and ready to go.
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Activation delays: when to contact the provider
Your communications provider agrees the activation date and owns the support conversation. Openreach says the Full Fibre service should be activated before midnight on that agreed date. If the date has not arrived, an inactive service is not necessarily a fault; complete the pre-checks and wait for the stated window. Openreach also says activation can still proceed as planned if you cannot complete the pre-checks.
If the service is still absent after the activation window:
- Contact the provider, not Openreach as a separate retail support channel.
- Quote the agreed activation date and the time you first checked after midnight.
- Give the exact ONT status: power, PON (solid/flashing/off), LOS (red/off) and LAN (on/off).
- State whether you tested two devices, a wired connection, the Ethernet cable and an ONT restart/reset.
- Ask the provider to check service provisioning and line status and to escalate to Openreach if its tests show an Openreach-side fault.
The provider is the party with the account, order and diagnostic access needed to investigate activation or authentication. Avoid placing a new order or repeatedly resetting equipment simply because the service has not appeared yet; establish whether the agreed date has passed and let the provider trace the order.
Choose the next action by fault domain
| Observed condition | Likely fault domain | Customer action | Escalation owner |
|---|---|---|---|
| No ONT lights | Power or ONT hardware | Check mains power and adaptor; do not move the fibre. | Broadband provider, potentially an engineer. |
| Flashing or off PON | Optical connection or network | Restart and reset in the documented order, then report the light state. | Broadband provider escalates to Openreach. |
| Red LOS | Optical loss of service | Stop at the power check; do not attempt fibre repairs. | Broadband provider/Openreach. |
| Solid PON, LAN off | Ethernet cable or router port | Reseat both ends and try a known-good cable or compatible router. | Provider if the link remains down. |
| Solid PON and LAN, no browsing | Router, Wi‑Fi, authentication or provisioning | Test two devices and one wired connection; report all results. | Broadband provider. |
| All lights normal before activation date | Provisioning may not yet be complete | Wait for the agreed date, then contact the provider if service is absent after midnight. | Broadband provider. |
What not to do
- Do not remove the ONT when you move home. Openreach records its serial number against the property, and the unit will not work at another address. Leave it mounted for the next occupant.
- Do not open the optical connection. Fibre components are not a self-repair job. A red LOS or persistent flashing PON needs provider diagnosis.
- Do not treat a cable as a cure-all. A replacement Ethernet lead addresses only the router link. It cannot restore an optical signal or accelerate activation.
- Do not keep power-cycling indefinitely. Perform the 30-second restart and one documented reset, record the resulting lights and let the provider investigate if the condition returns.
How to give support the information it needs
Have your order or account details ready, then describe the fault in a compact sequence: activation date; when the failure began; ONT power state; PON state; LOS state; LAN state; router WAN state; whether two devices and a wired test failed; and whether a second cable or router changed anything. This prevents the support conversation from restarting at generic Wi‑Fi advice when the evidence points to an optical or provisioning issue.
Keep the ONT powered and accessible while the provider tests it. If an engineer is arranged, do not remove the wall-mounted unit or alter the fibre route before the appointment. The provider can decide whether the evidence requires an Openreach visit or a router replacement.
Quick Recap
Quick decision checklist
- Is the agreed activation date still in the future? If yes, wait for the stated date and keep the equipment powered.
- Are there no ONT lights? Check mains power once and report it if the unit stays dark.
- Is PON flashing or off, or is LOS red? Record it, restart once, reset once as documented, then contact the provider.
- Is PON solid and LOS off? Check the WAN/FTTP Ethernet connection, test another cable, test two devices and try wired access.
- Does another router work? The original router is the likely fault.
- Has service still not appeared after midnight on the activation date? The provider must investigate and escalate where necessary.
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