Conditional tags in header file. Help appreicated

Hi people.
(website is http://www.myrevive.co.uk)
I am trying to remove the header images in some of the pages in my twenty eleven theme. I have managed to remove one on page 20 by using this

<?php if( !is_page( 20 ) ) : ?>'
and '<?php endif; ?>' wrapped around this:-
'<?php
// Check to see if the header image has been removed
$header_image = get_header_image();
if ( $header_image ) :
// Compatibility with versions of WordPress prior to 3.4.
if ( function_exists( 'get_custom_header' ) ) {
// We need to figure out what the minimum width should be for our featured image.
// This result would be the suggested width if the theme were to implement flexible widths.
$header_image_width = get_theme_support( 'custom-header', 'width' );
} else {
$header_image_width = HEADER_IMAGE_WIDTH;
}
?>

[Moderator Note: Please post code or markup snippets between backticks or use the code button.]

BUT i want to add other pages ID’s to this conditional tage. So it gives me the option to remove headers on pages I want.

Ive tried using this ‘<?php if( !is_page( array( 14, 20 ) ) : ?>’

but it does not seem to work. Can someone please let me know what I am doing wrong with this?

Thanks in advance

Kind regards
website is http://www.myrevive.co.uk