Downloading large files(~150MB) from FTP server hangs

I am trying to download files from ftp server with this code:

using (System.IO.FileStream fileStream = System.IO.File.OpenWrite(filePath))
              {

                byte[] buffer = new byte[4096];

                int bytesRead = responseStream.Read(buffer, 0, 4096);
                while (bytesRead > 0)
                {
                  fileStream.Write(buffer, 0, bytesRead);                      
                  bytesRead = responseStream.Read(buffer, 0, 4096);
                }

              }

The creation of responseStream:

System.IO.Stream responseStream = GetFileAsStream(url, username, password, false);

public static System.IO.Stream GetFileAsStream(string ftpUrl, string username, string password, bool usePassive)
{
  System.Net.FtpWebRequest request = (System.Net.FtpWebRequest)System.Net.WebRequest.Create(ftpUrl);
  request.KeepAlive = false;
  request.ReadWriteTimeout = 120000;
  request.Timeout = -1;
  request.UsePassive = usePassive;

  request.Credentials = new System.Net.NetworkCredential(username, password);

  request.Method = System.Net.WebRequestMethods.Ftp.DownloadFile;

  System.IO.Stream fileResponseStream;


  System.Net.FtpWebResponse fileResponse = (System.Net.FtpWebResponse)request.GetResponse();



  fileResponseStream = fileResponse.GetResponseStream();

  return fileResponseStream;
}

It works fine with smaller files but when a file is bigger (e.g. 150mb) the process hangs. For some reason the program does not understand that it has completed the download and it still tries to read more bytes.

I prefer answers which do not include using external libraries. Thank you