Remove a post type from search results, but keep all others

remove-post-type-from-search-results.php

<?php
/**
 * Modify query to remove a post type from search results, but keep all others
 * 
 * @author Joshua David Nelson, josh@joshuadnelson.com
 * @license http://www.gnu.org/licenses/gpl-2.0.html GPLv2+
 */
add_action( 'pre_get_posts', 'jdn_modify_query' );
function jdn_modify_query( $query ) {
	
	// First, make sure this isn't the admin and is the main query, otherwise bail
	if( is_admin() || ! $query->is_main_query() )
		return;
	
	// If this is a search result query
	if( $query->is_search() ) {
		// Gather all searchable post types
		$in_search_post_types = get_post_types( array( 'exclude_from_search' => false ) );
		// The post type you're removing, in this example 'page'
		$post_type_to_remove = 'page';
		// Make sure you got the proper results, and that your post type is in the results
		if( is_array( $in_search_post_types ) && in_array( $post_type_to_remove, $in_search_post_types ) ) {
			// Remove the post type from the array
			unset( $in_search_post_types[ $post_type_to_remove ] );
			// set the query to the remaining searchable post types
			$query->set( 'post_type', $in_search_post_types );
		}
	}
}

remove-post-types-from-search-results.php

<?php
/**
 * Modify query to remove a post type from search results, but keep all others
 * 
 * @author Joshua David Nelson, josh@joshuadnelson.com
 * @license http://www.gnu.org/licenses/gpl-2.0.html GPLv2+
 */
add_action( 'pre_get_posts', 'jdn_modify_query' );
function jdn_modify_query( $query ) {
	
	// First, make sure this isn't the admin and is the main query, otherwise bail
	if( is_admin() || ! $query->is_main_query() )
		return;
	
	// If this is a search result query
	if( $query->is_search() ) {
		// Gather all searchable post types
		$in_search_post_types = get_post_types( array( 'exclude_from_search' => false ) );
		// Make sure you got the proper results, otherwise bail.
		if ( ! is_array( $in_search_post_types ) ) {
			return;
		}
		
		// The post types you're removing, in this example 'page' and 'post'
		$post_types_to_remove = array( 'post', 'page' );
		
		// loop through each one and remove it from the searchable post types, if it's in there.
		foreach ( $post_types_to_remove as $post_type ) {
			// Confirm if the post type is in the results
			if( in_array( $post_type, $in_search_post_types ) ) {
				// Remove the post type from the array
				unset( $in_search_post_types[ $post_type ] );
			}
		}
		
		// set the query to the remaining searchable post types
		$query->set( 'post_type', $in_search_post_types );
	}
}