Diagnosis
A solid amber status light means the router is powered on but failed its startup sequence. It's likely stuck in a boot loop or corrupted its firmware during an update.
How to Fix It
First, unplug the router's power adapter from the outlet. Wait a full 60 seconds—this is crucial to let all capacitors drain. While it's unplugged, also disconnect any Ethernet cables from the WAN and LAN ports. Plug just the power back in and wait. A successful boot will show the light cycle through colors and settle on a steady blue. This can take up to 3 minutes.
If That Didn't Work
If it's still stuck on amber, you'll need to try a factory reset. With the router on, locate the tiny reset button on the back. Use a paperclip to press and hold it for about 10 seconds until you see all the front LEDs flash. The router will reboot to factory defaults, and you'll need to set it up again from scratch via the Tether app.
Heads Up
If it keeps reverting to amber after a factory reset, there might be a hardware fault. Contact TP-Link support—the BE800 has a two-year warranty.