We check this website, now knx-user-forum.de is up and dont blocked for our system and other users of the Internet.
So, answer to question: Is knx-user-forum Down Right Now? - NO! knx-user-forum is up!
If you have problem with access to site knx-user-forum, and domain knx-user-forum.de is not avalible.
Clear browser cache and/or try other web browser
(Chrome, Firefox or Safari).