Systemd does not restart service, although Restart=always

Here is my unit file of a systemd service:

[Unit]
Description=Tunnel For %i
After=network.target

[Service]
User=autossh
ExecStart=/usr/bin/autossh -M 0 -N -o "ExitOnForwardFailure yes" -o "ConnectTimeout=1" -o "ServerAliveInterval 60" -o "ServerAliveCountMax 3" -R 40443:installserver:40443 -R 8080:installserver:8080 tunnel@%i
Restart=always

[Install]
WantedBy=multi-user.target

The unit failed 15 days ago and systemd did not restart it, although "Restart=always" is in above unit file.

Here the status output of this service:

salt:/srv # systemctl status autossh@eins-work
[email protected] - Tunnel For eins-work
      Loaded: loaded (/etc/systemd/system/[email protected]; enabled)
      Active: failed (Result: start-limit) since Wed, 2016-02-10 14:33:34 CET; 2 weeks and 1 days ago
    Main PID: 17980 (code=exited, status=0/SUCCESS)
      CGroup: name=systemd:/system/[email protected]/eins-work

Feb 10 14:33:34 salt systemd[1]: Stopping Tunnel For eins-work...
Feb 10 14:33:34 salt systemd[1]: Starting Tunnel For eins-work...
Feb 10 14:33:34 salt systemd[1]: Failed to start Tunnel For eins-work.
Feb 10 14:33:34 salt systemd[1]: Unit [email protected] entered failed state

Related: https://serverfault.com/a/563401/90324

How to configure a systemd service to always restart if something fails?

The service failed to start too many times in a row, and so systemd gave up trying. This is what Result: start-limit means.

Note that units which are configured for Restart= and which reach the start limit are not attempted to be restarted anymore; however, they may still be restarted manually at a later point, from which point on, the restart logic is again activated. Note that systemctl reset-failed will cause the restart rate counter for a service to be flushed, which is useful if the administrator wants to manually start a unit and the start limit interferes with that.

You should resolve the problem that is causing the service to fail to start.

If you need to tune how many times and how quickly systemd attempts to restart a failing service, see the StartLimitInterval=, StartLimitBurst= and StartLimitAction= options.