Viessmann Weather Compensation

2 Viessman engeineers have told me that is you use WC, the system WILL NOT use the temp sensor in your normal wall mounted control.
Instead it knows the room temperature by looking at the return water temp to know when the room has reached the correct temperature
This sounds totally insane to me.
Am I missing somehting?
Or are they?

kevinleesmith said:

2 Viessman engeineers have told me that is you use WC, the system WILL NOT use the temp sensor in your normal wall mounted control.
Instead it knows the room temperature by looking at the return water temp to know when the room has reached the correct temperature
This sounds totally insane to me.
Am I missing somehting?
Or are they?

Click to expand...

I think a "normal" on/off roomstat will still just switch off the boiler if the roomtemp exceeds the stats setpoint temperature, if you want WC only, just set the roomstat higher so that it will not switch off the boiler. My OT often drops by 5/7C overnight but my roomtemp by less than 2C (with boiler shutdown) so difficult to see how one can get steady room temperature control on WC only as it only controls the boiler target flow temp. Return temp control is primarily used to enhance boiler efficiency, the lower the better, on the newer models Vaillants, it can be selected as "temperature spread" in the pump hydraulics menu and is settable between 10C & 20C, it achieves this by increasing/decreasing the pump speed.