cache pages forever

Hello,

I’m trying to cache all site pages with no time limit but even if i put a big interval for garbage collection or zero to disable it, I still get the page not from cache when I first enter site after few minuets. It seems that it is 1800 seconds or something like this no meter what I do.
Do you have an idea what am I doing wrong?
This is my site http://n7jlm.co.il/
I’m using this preload : “Refresh preloaded cache files every 0 minutes”
using mod_rewrite
and this for garbage collection:

Cache Timeout: 0 seconds
Timer:600 seconds
Check for stale cached files every interval seconds.
Clock: 00:00 HH:MM
Interval: Once Monthly

Thank you,
Uri