Redirect user - headers based on session variables

Ok, so my below code gives me headers already sent error, as i'm using header location more than once, but it shows what i'm trying to do at least. 

<?php 


session_start(); 
$user_id = $_SESSION["user"]["user_id"];


$loc1 = header("Location: page1.php");
$loc2 = header("Location: page2.php");


if ($user_id === 1008)
{$loc1;}
if ($user_id === 2)
{$loc2;}


?>