These models have a great lock for children to prevent any accidental adjustments. You know that you have activated the child-lock if you are unable to change the temperature or the power source. You can either permanently deactivate or temporarily override the lock - please see below:
Temporarily Override the Child-lock:
Push the control knob 3 times within 1.5 seconds
The lock will be reactive again after 10 seconds without touching the control knob
Permanently Deactivate the Child-lock:
Start with doing a temporarily override, after that simply turn off the child lock in the settings menu