nbn box lights ยท flashing
The lights on my nbn box are flashing
Flashing worries people more than it should. On several of these boxes a flashing light means data is moving, or that a firmware update is running, and switching the box off during an update is worse than whatever sent you looking.
Last reviewed: 15 August 2026 · by Alien IT Solutions
The short version
Before you restart anything, find out whether the flashing you are seeing is a fault or a normal state. On the FTTP box a slowly flashing green Optical light simply means data is moving. On HFC, flashing Downstream or Upstream lights mean a firmware update is running and nbn asks you to allow up to 10 minutes for it to finish.
That last one matters. Services that ride on the connection, including some medical alarms, can stop working during an update, which is why nbn suggests keeping a charged mobile handy rather than pulling the power out.
FTTP
| Light | State | What it means | What to do |
|---|---|---|---|
| Power | Green, slow flashing | The box is starting up. | Wait. It should settle to solid green shortly. |
| Power | Green, fast flashing | The box is being upgraded or is receiving updates. | Wait. Do not switch it off partway through an update. |
| Optical | Green, slow flashing | There is activity on the connection and data is moving. | Nothing to do. This is normal, not a fault. |
| Voice (UNI-V), if you have a phone service on the box | Green, flashing | A telephone has been off the hook for more than an hour. | Walk around and check every handset in the house, including cordless ones sitting crooked on the base. A handset left off the hook is a real fault that looks like a line problem. |
FTTC
| Light | State | What it means | What to do |
|---|---|---|---|
| Connection | Blue, blinking | The device is starting up. | Wait for setup to finish, which can take up to 20 minutes, and the light should go solid blue. |
| Connection | Solid red, or blinking red | There may be a line fault or a problem with the connection device. | nbn's instruction here is specific and unusual: turn the power to the connection device off, then contact your provider. Do not leave it powered while you wait. |
| DSL | Blue, blinking | Synchronising, or a software update is running. | Wait for it to go solid blue. |
| LAN | Blue or amber, solid or blinking | Data is flowing between the connection device and your router. | Nothing to do. |
HFC
| Light | State | What it means | What to do |
|---|---|---|---|
| Power | Green, flashing | There is an issue with your connection box. | This is a fault, not a startup state. Contact your provider. |
| Downstream | Green, flashing | A firmware update is running. | Allow up to 10 minutes. Services that ride on the connection, including some medical alarms, can stop working during an update, so keep a charged mobile handy. |
| Upstream | Green, flashing | A firmware update is running. | Allow up to 10 minutes, as above. |
FTTN and FTTB
There is no nbn connection box on FTTN or FTTB. nbn states plainly that these connections use a modem supplied by your provider, plugged into a telephone wall socket. So if you came here looking for the meaning of a light on an nbn box, you will not find one, because you do not have that box.
Before you touch anything
- Do not go up a ladder or onto a roof. That includes fixed wireless antennas and dishes. nbn's own fixed wireless guide tells you to contact your provider rather than touch an outdoor unit mounted more than 2 metres off the ground. There is nothing you can fix up there that is worth a fall.
- Do not open the nbn connection box, and do not touch the pit or the lead-in cable. That equipment belongs to nbn, not to you or your provider. Fibre terminations carry laser light that you cannot see and should not look into. Opening it can also end your service and leave you liable for the repair.
- Leave the backup battery alone beyond what your provider's own script tells you. If you have the optional Power Supply with Battery Backup, follow your provider's instructions for it and nothing more.
- Burning smell, scorch marks, or a modem too hot to touch: stop. Switch it off at the wall, unplug it, and do not plug it back in. Tell your provider it needs replacing. There is no troubleshooting step that comes before this.
Where this comes from
Every light state and every figure on this page comes from the sources below, each checked on 15 August 2026. Where a provider's guide disagrees with nbn's, the provider is describing their own hardware and you should follow theirs.
While you are on the phone to them anyway
Most people only look hard at their telco account when something has gone wrong. Since you are already dealing with them, send the bill over. The audit is free, and we will tell you plainly where you are overpaying and what is worth challenging.
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