Error document (404) not working

Error document (404) not working

The following is my htaccess code, please advise on what I'm doing wrong.
Thank you. I'm trying to add an error document. The 404 is in the root
directory of the site.
ErrorDocument 404 /404.html
<FilesMatch "\.(jpg|jpeg|png|gif|swf|ico|css|js)$">
Header set Cache-Control "max-age=604800, public"
</FilesMatch>
AddDefaultCharset UTF-8
AddLanguage en-US .html .htm .css .js
#Header unset ETag
FileETag none
<IfModule mod_headers.c>
<FilesMatch "\.(js|css|xml|gz)$">
Header append Vary: Accept-Encoding
</FilesMatch>
</IfModule>
<IfModule mod_mime.c>
AddType application/javascript js
AddType application/vnd.ms-fontobject eot
AddType application/x-font-ttf ttf ttc
AddType font/opentype otf
AddType application/x-font-woff woff
AddType image/svg+xml svg svgz
AddEncoding gzip svgz
</Ifmodule>
#Gzip
<ifmodule mod_deflate.c>
AddOutputFilterByType DEFLATE text/text text/html text/plain text/xml
text/css application/x- javascript application/javascript
AddOutputFilterByType DEFLATE image/x-icon image/svg+xml
application/vnd.ms-fontobject application/x-font-ttf font/opentype
</ifmodule>
#End Gzip