FtpWebRequest 30 minute time out

Probably you should try another implementation of FTP protocol client that isn't built on top of the FtpWebRequest.

Related issues exist for a long time, they don't have a clear solution or answer. So I would try something like FluentFTP, it uses Winsock API directly. XML Documentation Comment states that DownloadFile() should handle large file downloads well:

/// <summary>
/// Downloads the specified file onto the local file system.
/// High-level API that takes care of various edge cases internally.
/// Supports very large files since it downloads data in chunks.
/// </summary>

For more information check:

• Downloading large files(~150MB) from FTP server hangs discussion on StackOverflow
• FtpWebRequest is Broken article by Matt Mitchell
• Winsock API page on Microsoft TechNet
• Source Code section in Partial FTP Downloader article by Elmue