In the Netherlands we have central heating boilers that often communicate with the thermostat using Opentherm protocol. Unfortunately, most thermostats that have apps only have an on/off function. Is it possible to make a thermostat with opentherm protocol?
That will never happen, their thermostats are prehistoric. Do yourself a favour and buy a decent thermostat with opentherm that is chronologic. I’ve been using the NSPANEL and NSPANEL pro for thermostats and they a awful 
It strikes me that all Chinese thermostats are prehistoric. Some people have a Modbus connection, but my boiler cannot use that. It would be really nice if @Sonoff makes a thermostat that works on opentherm and modulates.
I am using TH16 and it works great already several years. I attached the temp sensor to the boiler and other temp sensitive devices that I have and control it according the the real time temperature. Do not forget to add a relay in case you need to drive high current device.
So I don’t want a situation with an on/off principle. This concerns a CV. boiler. Opentherm takes care of the central heating. boiler modulated. That is not possible with an on/off system
Also there is no anticipation, it waits for a temperature to drop below a set point instead of seeing ‘it’s going to drop below the set point in 10 minutes I will anticipate this and switch on’ to give a much better heat curve