!!
critical Velux
Error Code Yellow LED on continuously/permanently
Indicates the backup batteries are not connected or defective; also may indicate a faulty main supply fuse.
? What Causes This
Malfunction in the power system.
✓ How to Fix It
Ensure proper installation of replacement batteries if necessary. Replace control circuit board if required.
Source: page 68 of the official manual
From the manual
This error code appears in:
Velux Kfx 210