Help with Session timeout redirect

I have an application and I am trying to code it so that when I have a session timeout and a user clicks in the application they get redirected to a session timeout web page. This page has a button that allows the user to return to the application(restart a session in the application)

All of my code works up until I try to redirect them back to the application start page...at that point it just detects that the session has timedout and redirects them back to the session timeout page.

I guess what I am trying to figure out is how to restart the session if the session has timed out...but I need to do it on a button click.

Below is the relevant code.

Default aspx.cs has this

    public partial class _Default : SessionCheck
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            SessionCheck.RedirectUrl = "SessionTimeout.aspx";
        }

The Session Check class is as follows

public class SessionCheck : System.Web.UI.Page
    {
        /// <summary>  
        /// property vcariable for the URL Property  
        /// </summary>  
        private static string _redirectUrl;

        /// <summary>  
        /// property to hold the redirect url we will  
        /// use if the users session is expired or has  
        /// timed out.  
        /// </summary>  
        public static string RedirectUrl
        {
            get { return _redirectUrl; }
            set { _redirectUrl = value; }
        }

        public SessionCheck()
        {
            _redirectUrl = string.Empty;
        }

        override protected void OnInit(EventArgs e)
        {
            //initialize our base class (System.Web,UI.Page)  
            base.OnInit(e);
            //check to see if the Session is null (doesnt exist)  
            if (Context.Session != null)
            {
                //check the IsNewSession value, this will tell us if the session has been reset.  
                //IsNewSession will also let us know if the users session has timed out  
                if (Session.IsNewSession)
                {
                    //now we know it's a new session, so we check to see if a cookie is present  
                    string cookie = Request.Headers["Cookie"];
                    //now we determine if there is a cookie does it contains what we're looking for  
                    if ((null != cookie) && (cookie.IndexOf("ASP.NET_SessionId") >= 0))
                    {
                        //since it's a new session but a ASP.Net cookie exist we know  
                        //the session has expired so we need to redirect them  
                        Response.Redirect("SessionTimeout.aspx?timeout=yes&success=no");
                    }
                }
            }
        }
    }

And finally the code on the button click where I am trying to restart the session and the application...

        protected void btnReturn_Click(object sender, EventArgs e)
        {
            Response.Redirect("Default.aspx");
        }

My guess is I need something in this response redirect to restart the session btu I dont know what that would be