Restarting Interval not working after clearing

I am getting num1 and num2 value from service call. I am trying reset interval after clearing it but it does not work this way. I have also tried other ways mentioned in stackoverflow. Nothing works.

function func(){    
     if (num1 > num2 ) {
          console.log(" gt greater than lt");
          clearInterval(interval);
          flag = true;
          setInterval(func,1800000);
          $('.class').trigger('point');
          return;

        }
//do something
}

var interval = setInterval(func,10);