The internet dies, and the first thing people look at is the row of lights on the modem. The trouble is that the labels are abbreviations that explain nothing to a layperson: PON, LOS, WAN, WLAN.
Yet that row of lights gives the quickest answer available. It tells you exactly where the connection broke, inside the house, or outside. And that decides whether you need to call the provider or simply unplug one cable.
Three principles that hold across almost every brand
Before memorising them one by one, these three patterns already explain most situations:
- Steady on generally means the connection is established and stable.
- Fast, irregular blinking means data is flowing. This is normal, even a good sign.
- Slow, evenly timed blinking means the device is trying to establish a connection and has not succeeded.
Red almost always means something is wrong. Completely off can mean the feature is switched off, not broken.
What each light means
| Label | Indicates | Normal state |
|---|---|---|
| POWER / PWR | Mains power present | Steady on |
| PON | Modem registered on the fibre network | Steady on |
| LOS | Loss of fibre light signal | Off |
| INTERNET / WAN | Address obtained from the provider | On or blinking |
| LAN / ETH | A cable is connected to the port | Blinks during use |
| WLAN / Wi-Fi / 2.4G / 5G | The wireless radio is active | Blinks during use |
| WPS | Quick-pairing mode is running | Off |
| TEL / PHONE | Telephone service | On if subscribed |
Note the LOS row. Unlike the others, its normal state is off. This light only comes on when there is a problem, which is why many people first notice it exists when it turns red.
A red LOS light, the most asked about
LOS stands for Loss of Signal. Your fibre modem is no longer receiving light from the provider's network.
This is important to grasp: the problem is on the fibre path, not in Wi-Fi. Restarting the router, changing the password, or reconfiguring the device will change nothing.
What you can check yourself, in order of likelihood:
Check for bends in the fibre cable
Fibre cable is far more fragile than LAN cable. A sharp bend, pinched under a table leg, or kinked behind a cabinet, is enough to cut the light even though the cable looks intact from outside.
Unplug and refit the connector
Remove the fibre connector from the modem, inspect the tip, then refit it until it clicks. Do not touch the fibre end with your fingers; oil from skin can block the light.
Switch the modem off for a few minutes
Unplug it from the mains, wait about two minutes, then power it back on. If LOS goes out and PON goes steady, the connection has recovered.
Ask a neighbour on the same provider
If they are affected too, this is a fault at the provider and there is nothing to do beyond reporting it.
If all four have been tried and LOS is still red, the problem is outside the house, on the distribution cable, a terminal on the pole, or the provider's equipment. Call customer service and say the LOS light is red. Using that term usually speeds things up, because the technician immediately knows the class of fault.
Reading combinations of lights
| What you see | What it means | What to do |
|---|---|---|
| All off | No power | Check the adapter and the socket |
| Only POWER on | Modem alive but not yet connected | Wait 2 minutes, then check LOS |
| LOS red | The fibre path is broken | Follow the four steps above |
| PON blinking slowly | Trying to register | Wait; if over 5 minutes, report it |
| PON steady, INTERNET off | Fibre fine, authentication failed | Usually an account issue, call the provider |
| All normal, Wi-Fi light off | The wireless radio is switched off | Press the WLAN button or check for a schedule |
| All normal but the internet is slow | Not a connection problem | See the slow Wi-Fi guide |
The last row is often misread. If every light is normal, the connection to the provider is genuinely healthy. The slowness you feel comes from elsewhere, the number of devices, a congested channel, or the router's position. The order to check is in the guide to fixing slow Wi-Fi.
When the Wi-Fi light is off but everything else is normal
This is not a fault. The wireless radio can be switched off without switching off the modem, and it happens more often than people expect:
- The WLAN button on the modem was pressed by accident while cleaning.
- An automatic schedule is active, some routers can switch Wi-Fi off at certain hours.
- The feature was disabled from the provider's app on a phone.
- The modem was just reset to factory settings.
Hold the WLAN button for a few seconds. If the light returns and the network appears in the list, you are done. If the network stays invisible to one device only while the others are fine, the cause is with that device, covered in the guide to Wi-Fi problems on one device.
When the lights look normal but the connection keeps dropping
There is one situation the lights simply do not show: a connection that drops for a few seconds and recovers on its own. The lights often have no time to change because the interruption is too brief.
If that is what you have, watching the lights will not help. The causes and the order of checks are different, and covered separately in the guide to Wi-Fi that keeps disconnecting.
Before calling the provider
Three things make the call go far faster:
- Say which light is on and what colour. "LOS is red" is more useful to a technician than "my internet is down".
- Say since when. A sudden fault and one that degraded slowly are handled differently.
- Say what you have already tried. Particularly that the modem has been power-cycled, so you are not asked to repeat it.
If the complaint is about speed rather than a dropped connection, have speed test results taken the right way ready too, how to do that is in the guide to checking internet speed. Figures gathered carelessly are a common reason for a report being dismissed.
Frequently asked questions
The LOS light is red, what does that mean?
The modem is not receiving light from the provider's fibre network. The cause may be a bent or broken fibre cable, a dirty or loose connector, or a fault at the provider. This is not a Wi-Fi problem and it will not clear however many times you restart the router.
The internet light is off but Wi-Fi is still on. Why?
Wi-Fi and internet are two separate layers. Devices can still connect to the router, but the router itself has no route out to the internet. The symptom: the network shows full bars, but no page will open.
Why does one light keep blinking?
Fast, irregular blinking on the LAN or Wi-Fi lights is actually normal, it means data is flowing. What to be suspicious of is slow, evenly timed blinking on the PON or internet light, because that means the device is trying and failing.
