Optolink not responding

I want to connect my Viessmann to Openhab2 (running on a Raspberry Pi). Using the binding and optolink looks the easiest way, so that’s the way I took.
Starting optolink in debug mode looks OK. It connects fine with the heating and the debugger stops with the message it’s waiting for a broadcast on port 31113. So far so good.
But opening a putty on that port (in raw-mode) doesn’t work. I don’t receive an answer, and the debug-window from optolink doesn’t show a connection. Putty stops after a while saying the connection timed out. Trying to use other ports or whatever doesn’t help. Also the binding doesn’t work, but that’s obvious as it’s using the same port.
Someone an idea on how to open this connection?