RS-485 bus thermostat for therm working with Homey?

I’m searching for a solution to make my therm smarter to work with Homey and the connected thermostats.

Current sitation:

  • Sieger therm BK11 with CRC51 thermostat (wired) with RS-485 bus system
  • Eurotronioc thermostats connected to Homey (controlled with Homey Heating Scheduler app)
    Before adding the Eurotronic thermostats, the CRC51 controlled the therm using inside and outside temperature and programmed heating times.
    After adding the Eurotronic thermostats, the CRC51 thermostat only controls heating using the outside sensor and the programmed heating plans. The CRC51 room thermostat can’t be used because if the Eurotronics are closed and the target room temperature is not reached, the therm will heat up without changing room temperature.
    The term has its own heating program (days, time for heating) and don’t react on heat requests from radiator thermostats.

Target situation:

  • I want to exchange the CRC51 with another RS-485 thermostat whis supports wlan/Z-Wave/ZigBee functionality to connect it to Homey (or the Eurotronic thermostats to the new central one).
  • The thermostats at the radiators should request heat from the therm if needed. If temperature of all thermostats is reached, the therm should not heat up (except of outside temperature below 3°C).
  • The CRC51 controls water heating with programmed times (days and times for heat up the water). This should also be possible with a new thermostat.

Sieger (and Buderus) have no device or replacement for older therms.
Tado or other provider don’t support Sieger. I don’t know if they don’t suport RS-485 in general. It seems they only support old therms with only a on/off control, not a programmable bus systems.

My questions:

  • Does anyone know a replacement of the CRC51 thermostat with WLAN or Z-Wave/Zigbee for making the therm smart? At least for controlling with another app? I have seen some chinese products but I cant see if it could be compatible.
  • Is it possible to control the therm using the state of the Eurotronic thermostats?

I know, this is a speacial situation, but perhaps someone of the Homey specialists have experience with such therm systems.