PHP update adds new record with an id of 0

This is my first time so please be patient with me. I have tried and tried without success! My database has 7 fields with the last one being 'id' as key and auto increment I am trying to update one or all of the fields in 1 record only. However I just get a new record with all previous data except id is incremented by 1. This is my code:

<?php
$error = '';
ini_set('display_errors', 1);
session_start();
if(!isset($_SESSION['login_user'])){ // If session is not set then    redirect to Login Page
header("Location:Login.php");  
}
// grab connection code
$login_id = $_SESSION['login_id'];
include "connection.php";
$query = "SELECT * FROM bvoa_login WHERE id = '$login_id'";
// get result
$result = $conn->query($query);
//create array of result
$row = $result->fetch_assoc();
// set existing data into variables
$curr_name = $row["name"];
$curr_username = $row["username"];
$curr_email = $row["email"];
$curr_property_no = $row["property_no"];    
$curr_website = $row["website"];    
if($_SERVER["REQUEST_METHOD"] == "POST") {
    if (!empty($_POST['username']) && !empty($_POST['email'])
        && !empty($_POST['new_password']) && !empty($_POST[  'password_confirm']) && !empty($_POST['location']) && !empty($_POST['real_name'])){
        $username = $_POST['username'];
        $real_name = $_POST['real_name'];
        $email = $_POST['email'];
        $new_password = $_POST['new_password'];
        $password_confirm = $_POST['password_confirm'];
        $location = $_POST['location'];
        $website = $_POST['website'];
        // compare passwords...
        if (strcmp($new_password, $password_confirm) == 0){
            $password_hash = sha1($new_password);
            $query = "UPDATE `bvoa_login` SET `username`='$username' WHERE `id`='$login_id'";
            $result = $conn->query($query);
        }else{
            $error = "Passwords do not match.";     
    }
    }else{  
    $error = "You must enter all fields to continue.";
    }
$conn->close();
}

?>