Main page don’t cached normaly.

WP Super Cache don’t cash main page normaly. Main page dissapear from cache after 600 seconds. Settings: cache time out: 16000 seconds, check for stale cashed files: daily. When I use preload function, all pages cashed except main page. Main page cashed only when visit it, and dissapear from cache in 600 seconds.

How do I get the main page to be cached like all others?