Diagnosis
A hardware or severe connection failure. Solid red means the unit cannot establish any functional network link.
How to Fix It
Unplug the red-light unit. Also unplug its power adapter from the wall. Wait 2 full minutes. Reconnect only the power adapter to the wall, then plug the Deco unit into it. Wait 5 minutes for it to complete its boot sequence.
If That Didn't Work
The unit may have failed. Perform a factory reset. Locate the reset button on the bottom. With the unit powered on, press and hold it for about 10 seconds until the LED flashes amber. Release. You must then re-add it as a new unit in the Deco app.
Heads Up
Do not interrupt the boot process after a reset. The LED will cycle through colors for several minutes. Only intervene if it settles on solid red again, which indicates a hardware fault requiring replacement.