CPT Template Not Showing – Getting 404

Always flush the rewrite rules when you register a new public post type or taxonomy. Otherwise the internal rewrite rules will not take that into account when an URL is mapped to a query.

You can automate that process by hooking into registered_post_type and registered_taxonomy.

Below is the updated code, based on feedback from comments and other people.

Download as plugin T5 Silent Flush on GitHub.

add_action( 'registered_post_type', 't5_silent_flush_cpt', 10, 2 );
add_action( 'registered_taxonomy',  't5_silent_flush_tax', 10, 3 );

/**
 * Flush rules for custom post types.
 *
 * @wp-hook registered_post_type
 * @param   string $post_type
 * @param   stdClass $args
 * @return  void
 */
function t5_silent_flush_cpt( $post_type, $args )
{
    if ( $args->_builtin )
        return;

    if ( ! $args->public )
        return;

    if ( ! $args->publicly_queryable )
        return;

    if ( ! $args->rewrite )
        return;

    $slug = $post_type;

    if ( isset ( $args->rewrite['slug'] ) && is_string( $args->rewrite['slug'] ) )
        $slug = $args->rewrite['slug'];

    $rules = get_option( 'rewrite_rules' );

    if ( ! isset ( $rules[ $slug . '/?$'] ) )
        flush_rewrite_rules( FALSE );
}

/**
 * Flush rules for custom post taxonomies.
 *
 * @wp-hook registered_taxonomy
 * @param   string $taxonomy
 * @param   string $object_type
 * @param   array  $args
 * @return  void
 */
function t5_silent_flush_tax( $taxonomy, $object_type, $args )
{
    // No idea why we get an array here, but an object for post types.
    // Objects are easier to write, so ...
    $args = (object) $args;

    if ( $args->_builtin )
        return;

    if ( ! $args->public )
        return;

    if ( ! $args->rewrite )
        return;

    $slug = $taxonomy;

    if ( isset ( $args->rewrite['slug'] ) && is_string( $args->rewrite['slug'] ) )
        $slug = $args->rewrite['slug'];


    $rules = get_option( 'rewrite_rules' );

    if ( ! isset ( $rules[ $slug . '/(.+?)/?$'] ) )
        flush_rewrite_rules( FALSE );
}

This will flush the rules each time you create a new post type or taxonomy. No need to visit the permalink settings again.