If your VELUX Blackout Roller Blind is not working or you believe it to be faulty, it could just be that the cord is twisted or not positioned correctly, meaning the blind will not roll up and down correctly. Please note, the cord should always be placed behind the plastic fixing just like the below images.
If the cord is twisted, please remove the side channels from each side and try and untwist before re-installing the side channels and re-attempting the operation. If the issue remains after this or you see the cord has frayed, please capture some images of the fault and contact our Customer Support Team at customerservices@itzala.com