nbn box lights ยท red
There is a red light on my nbn box
Red is the one that sends people looking, and it does not mean the same thing on every box. On some it is a genuine network fault worth reporting immediately. On one of them, nbn's documented instruction is to switch the device off before you call.
Last reviewed: 15 August 2026 · by Alien IT Solutions
The short version
A red indicator is worth taking seriously, but the specific meaning depends entirely on which box you have in front of you. Below is every state that nbn documents as a fault on each technology, along with the action nbn itself gives.
One of these is unusual and worth reading even if you skim the rest. On fibre to the curb, a solid or blinking red Connection light comes with an instruction to turn the power to the connection device off and then contact your provider, rather than leaving it running while you wait.
FTTP
| Light | State | What it means | What to do |
|---|---|---|---|
| Optical | Red | Your connection box has lost its connection to the nbn network. | This is the one that matters. It is a network side fault. Contact your provider, tell them the optical light is red, and ask them to raise it with nbn. |
| Alarm | Red | The box has a fault and is not working normally. | Contact your provider and quote the alarm light. The box is nbn equipment, so replacing it is their job to arrange. |
FTTC
| Light | State | What it means | What to do |
|---|---|---|---|
| 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. |
| Connection | Alternating red and blue | There may be a line fault, such as a telephone left off the hook. | This one is often yours to fix. Unplug every phone, fax, alarm dialler and anything else from every telephone wall socket in the house, then look again. If the light clears, plug them back one at a time until it returns and you have found the culprit. |
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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