Tado - OpenTherm issues

Hi,

I recently replaced my boiler with an OpenTherm setup. I'm having issues with big temperature drops whenever most of the heating is turned off. I hope someone can shed a light on what might be wrong.

- Setup:

○ Wired smart thermostat connected to Bosch GC 7000iW-28 C with Bosch Opentherm convertor EMS-OT (7746901847)

○ 5 SMT's configured to use the wired smart thermostat as zone controller


- Issue:

○ When multiple SRTs request heat, the boiler goes into full power and rooms heat up quickly

○ When only one SRT requests heat, the room heats up slowly with 'medium' boiler acivity, which still makes sense since it's meant to be economical

○ When all thermostats but one stop requesting heat, the remaining room slowly cools down and the boiler will only activate after a 2-3 °C temperature drop. This highly unconfortable in my home-office situation.


- Workaround: 

○ Turning on other Smart Thermostat -which is only meant to be a controller in this setup- to a (much) higher temperature than the actual room temp triggers the boiler to go full power resulting in the single room back up to the temperature.


- Question:

○ Is this normal OpenTherm behavior or is something wrong with the setup?

○ Could it be this is because my boiler is no longer detecting cooler return water and therefore kicking in too late?

○ Could this be a Tado - OpenTherm or Boiler issue?


I'm adding a picture that clearly illustrates my issue


Thanks for your help!