Cant Seem to figure this out please help?

This isn't working for some reason any idea's of why?

var Pos = $('html, body').scrollTop();

if (Pos==0){

     Scroll();

}

var Bottom = $('html, body').scrollTop();

if (Bottom==2000)

{

     $('html, body').animate({scrollTop:0}, 'slow');

}

function Scroll() {

$("html, body").animate({ scrollTop: $(document).height() }, 20000);

its a scroll it auto scrolls to the bottom and it reaches 2000px its ment to scroll back up to 0px but it isn't :/

Any idea's thank you !

}