Try this
function wpse66115_redirect_to_sub_site() {
if ( is_main_site() ) {
if ( is_user_logged_in() ) {
} else {
exit( wp_redirect( 'http://old.heiledeg.no', 301 ) );
}
}
}
add_action( 'parse_request', 'wpse66115_redirect_to_sub_site' );