Show comments outside of WP

I’m displaying posts outside of WP using “the loop” – however – when I want to display the comments to each post, or the comments form, I can’t seem to manage.

I try to call comments_template() or using the comment templates tags such as comment_text() but only get on working and that is comments_popup_link(). (All inside of the loop)

I call the wp-blog-header.php on the external pages.

Thanks for any guidance in the right direction