windows service körs bara en gång!

varför körs inte koden var 30:e sekund för? den körs endast en gång sen händer inget mer! :(

        private Timer tmr;
        private bool Running = false;

        protected override void OnStart(string[] args)
        {
            tmr = new Timer(30000);
            tmr.Elapsed += new ElapsedEventHandler(OnTimedEvent);
            tmr.Enabled = true;
        }

        private void OnTimedEvent(object source, ElapsedEventArgs e)
        {
            if (Running == true)
                return;

            Running = true;

            StreamWriter sw = File.AppendText(RootDirectory + "log\\2006\\200621");
            sw.WriteLine("Skriver!!!");
            sw.Flush();
            sw.Close();

            Running = false;
        }

        protected override void OnStop()
        {
            tmr.Enabled = false;
        }