Accurate flow measurement is typically a lot harder to achieve than temperature measurement, but if you just want to look at relative performance over time, or with different settings ‘close enough for government work’ works for me. 
It appears the newer-gen Arotherm devices have a built-in compensation for the sensors. There is an automatic air-bleeding program which detects sensor offsets and sets a delta internally to compensate. The older arotherms also have this program - maybe it would be worth a shot to try whether the compensation is an undocumented feature on them
1 Like
Very interesting! Where have you gleaned this info about the new-gen Arotherms?
I read that there is an air bleeding mode and temperature calibration on a german heat pump subreddit. Looking at the manual of the latest Vaillant indoor unit for the newer models confirms this:
The service instructions mention running the air bleeding program (“Entlüftungsprogramm”) to calibrate the sensors once a year.
More details in the document (German only, unfortunately)
2 Likes