From what you have described is Evohome controlling the UFH or is it operating in unconstrained operation? I would recommend that the UFH with your boiler would probably be better controlled using Vitodens add on module. It should not be left on unconstrained operation unless the full system is only Combi DHW and UFH.
The DHW temperature is adjusted through the menu function - up to 60 degrees (I think).
Pork Chops comments on Evohome with weather compensation are correct in my experience Evohome deals with the problem, provided that all other parameters are left unchanged.
I would not recommend converting to Open Therm operation until the current system is set up correctly. Your existing Evohome system can easily be configured to operate a Viessmann boiler through Open Therm, but not with the UFH in unconstrained mode
The DHW temperature is adjusted through the menu function - up to 60 degrees (I think).
Pork Chops comments on Evohome with weather compensation are correct in my experience Evohome deals with the problem, provided that all other parameters are left unchanged.
I would not recommend converting to Open Therm operation until the current system is set up correctly. Your existing Evohome system can easily be configured to operate a Viessmann boiler through Open Therm, but not with the UFH in unconstrained mode