I had this same issue, on one of my radiators it just never finished calibration, I tried twice.
The picture how to reset requires registration
I'll describe it in text:
1. Pry the plastic lid with buttons from the device using a screwdriver. There are groups of 2 and 4 pins on the circuit board underneath.
3. Touch the screwdriver to the two pins to short them. You may see a spark.
4. Remove the screwdriver and replace the plastic lid.
Calibration is OK after firmware upgrade!