Hello, I just stumpled upon this product and I like it. Can someone confirm if the thermostat communicates through the opentherm protocol with the boiler (CV)
i have a nefit with an opentherm converter and I would like the HestiaPI to control it (with modulation ofcourse)
Welcome to the club 
It seems as there are some solutions but you will need to check if they fit your setup.
Check here
https://pure-knowledge.nl/2017/02/21/openhab2-otgw-and-mqtt/
and here
Basically you will need to seek compatibility of OpenTherm (OTGW) with OpenHAB as HestiaPi is based on OpenHAB. Please post here your finding for others too.
ok, so for me this thermostat is a little bit of a mystery. is it compatible with any boiler/heater? if so, is it a modulating thermostat or just on/off?
The wired interface is simple relays. The logic controlling the relays can be more complex like PID etc.
The wireless interface though via WiFi adds support for various network protocols and allows intermediate gateways. This is where our knowledge stops. We try to offer an open platform, not tied to technology A or B. Specific technologies and integrations need to be supported by the OpenHAB and HestiaPi community.