Hello,
I’ve noticed that a component called opentherm_gw has been made, but from what I understand it can only really work if the GW is between an actual thermostat. Which not all of us have! (fyi nodeMCU version)
Before this component came out I made an AppDeamon app that can read data from the GW in standalone mode. It can also set the boiler water temperature for the central heating. Which i use via a PID loop to heat the house. This has only been tested via telnet.
https://github.com/matthew73210/python/tree/appdeamon_apps/home_assistant/AppDeamon
I’d be happy if you could port what I did into the component so it works for everybody else. I could also try and do a pull request but I don’t have the python/HA experience yet so I’ll probs pass for an ass.
It’s your call 
Matthew