WordPress：get_header（）在页面模板中不起作用

I am using page template to fetch data from a custom post type. page name is client and template name is client-template.php inside page-templates folder.

this is code in client-template .

<?php
/**
 * Template Name: Client Template
 *
 * @package WordPress
 * @subpackage Twenty_Fourteen
 * @since Twenty Fourteen 1.0
 */
?> 
<?php get_header();?>

<div id="main-content" class="main-content"> 
    <div id="primary" class="content-area">
        <div id="content" class="site-content" role="main">
            <?php
                                $args=array('post_type' => 'clients');
                                $query= new WP_Query($args);                               
                // Start the Loop.
                while ($query-> have_posts() ) : $query->the_post();

                                        echo the_title();
                                        echo the_post_thumbnail();


                endwhile;
            ?>
        </div><!-- #content -->
    </div><!-- #primary -->
</div><!-- #main-content -->

Now, this is fetching data and shows it. but, header is not getting included whats wrong here , I used types plugin to create post type and then selected above mentioned template for client page. Please help me with this.