Get all Posts If has same custom field values in Posts

Following code will be proper for the meta query.

  $query_args = array(
        'post_type'   => 'service',
        'posts_per_page' => -1,
        'meta_query'  => array(
            array(
                'value'   => $zip,
                'compare' => 'LIKE',
                'key'     => 'zipcode',
            ),
        )
    );
   $query = new WP_Query($query_args);
   <?php if ( $query->have_posts() ) :while ( $query->have_posts() ) : $query->the_post();  ?>
       <h3><?php the_title(); ?></h3>
   <?php endwhile; // end of the loop. ?>
   <?php wp_reset_query(); ?>
   <?php else: ?>
      No results found.
   <?php endif; ?>

Hope it helps.