Nest Thermostat

[TinkerDay]

Hi

I am on the steeping learning curve of OpenTherm and currently struggling to get a slave to master communication setup and working.

My hardware
Nest GenIII Smart Thermostat (Master)
Wemos D1 with an Opentherm Slave shield https://www.tindie.com/products/thehognl/opentherm-slave-shield-for-wemoslolin/

Code
https://github.com/ihormelnyk/opentherm_library/blob/master/examples/OpenThermSlave_Demo/OpenThermSlave_Demo.ino

Pin definitions
const int inPin = 4;
const int outPin = 5;

It looks like the code is running and talking to the shield as I do get a response (which freezes if I do remove opentherm wiring to Nest thermostat).

However , all I get on the serial monitor is
..T0
..Bf0000000
..T0
..Bf0000000
..T0
..Bf0000000

Also, the Nest Thermostat states that it cannot locate an OpenTherm device when scrolling through its setup menu.

Seems that there maybe a need for a handshake maybe?

Any help is appreciated or a pointer to a forum where there are similar users active online.

thanks in advance....