fastcgi_cache not caching

Hi,
In my nginx.conf in http section I got:

fastcgi_cache_path /var/cache/nginx/cache/heppler keys_zone=heppler:500m levels=1:2 inactive=600s max_size=100m;
fastcgi_temp_path /var/cache/nginx/fastcgi_temp;


In my server section I got:
location ~ \.php$ {
fastcgi_split_path_info ^(.+\.php)(/.+)$;
try_files $fastcgi_script_name =404;
fastcgi_pass unix:/var/run/php-fpm.sock;
fastcgi_param PATH_TRANSLATED $document_root$fastcgi_script_name;
fastcgi_index index.php;
fastcgi_read_timeout 300;
include fastcgi_params;
fastcgi_ignore_headers "Cache-Control";
fastcgi_cache heppler;
fastcgi_cache_key "$scheme$request_method$host$request_uri";
fastcgi_cache_valid 200 10s;
}

But I don't see any files in /var/cache/nginx/cache/heppler