T-Fiber router light is red

Router can't get an internet connection

On the Calix routers T-Mobile Fiber uses, a flashing red light means the router can't get an internet connection. A PON light that is red or off means there is a problem on the fiber line itself.

Is T-Fiber down right now? Operational: 7 problem reports in the last hour. If it were down for everyone, this problem could come from there; right now it looks normal.

Fix it

How to fix it

Check the WAN cable between the router and the ONT.
Unplug the router for 30 seconds, then plug it back in.
If you have a separate ONT box, unplug it for 10 seconds and give it 2 to 5 minutes after plugging it back in.
Contact T-Fiber support by chat if the light stays red or the PON light is red or off.

From T-Fiber's help pages: fiber.t-mobile.com, in our words. Checked on 5 November 2026. If the steps do not help, T-Fiber's own support is the next stop.

T-Fiber router light is red

How to fix it

More common T-Fiber problems