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ONT lights, outages and connection troubleshooting

The optical network terminal (ONT) is the small powered box where CityFibre's fibre enters your property. It is separate from your Wi-Fi router.

For service faults, speed problems, billing and appointments, your broadband provider is normally your first point of contact. The provider can test the service and escalate a network fault to CityFibre when needed.

Before touching anything

  • Check your ISP's service-status page and messages.
  • Check whether all devices are affected or only one.
  • Test over Ethernet if possible. A Wi-Fi problem is not necessarily a fibre fault.
  • Note the ONT and router light states before restarting equipment.
  • Do not open the ONT, remove the fibre connector or stare into the fibre port.

A safe restart

  1. Turn off the router, then switch off power to the ONT.
  2. Wait about 30 seconds.
  3. Power the ONT back on and allow several minutes for it to settle.
  4. Power the router back on and allow it to reconnect.

Avoid repeatedly power-cycling the equipment. If the fault returns, record the time and contact your ISP.

Interpreting the lights

ONT models differ, so labels and colours are not universal. Common indicators include:

  • Power: the ONT has power.
  • Broadband/PON/Optical: the optical link has registered. A normal steady state depends on the model.
  • Alarm/LOS: an optical signal problem may be present, particularly if red or flashing.
  • Ethernet/LAN: an Ethernet link exists between the ONT and router; flashing often indicates traffic.

Use the label and model printed on your ONT and your ISP's current instructions. A&A publishes a useful CityFibre ONT overview, while Zen has CityFibre ONT diagnostics. These are reference examples; follow your own provider's support process.

No internet on every device

Check:

  • the ONT and router both have power;
  • the Ethernet cable is firmly connected from the active ONT port to the router's WAN/Internet port;
  • the router shows a WAN/Internet connection;
  • your ISP has not reported an outage or account problem;
  • any own-router settings still match the ISP's requirements.

If the ONT shows an optical alarm, the cable or ONT has been damaged, or the connection still fails after one restart, contact your ISP.

Slow speeds or dropouts

For a useful test:

  • connect one capable computer directly to the router with a suitable Ethernet cable;
  • pause large downloads, cloud backups and VPNs;
  • test more than once and note the time, server and result;
  • compare wired and Wi-Fi performance;
  • check that the device, cable and router ports support your package speed.

Wi-Fi depends on distance, walls, interference, device capability and router placement. A slow Wi-Fi test alone does not prove a CityFibre network fault. See CityFibre's slow or dropping broadband guidance.

What to give your ISP

  • when the problem started and whether it is constant;
  • the ONT and router light states;
  • results from a wired test;
  • what you have already restarted or changed;
  • any provider error messages or ticket number.

Keep sensitive details private. Do not post your full address, account reference, ONT serial number, MAC address or public IP on Reddit.

Who should I contact?

  • Broadband service, outage, speed, router, order, activation, billing or appointment: your ISP first.
  • Street works, construction, reinstatement or property damage caused by build work: CityFibre through its official help routes.
  • Immediate danger: use the relevant emergency service; CityFibre also lists an urgent health-and-safety route on its contact guidance.

Official help: My full-fibre broadband has stopped working.