ERR opens actuator although it is too warm

±0.3° okay. The scaling on the control device corresponds approximately to 5°C steps (i.e.: 1: 5°C / 2: 10°C ... up to 6: 30°C). So at level 3 it should be about 15°C, but in the room it is 22°C, that is a difference of 7°C, the dial thermostats are not that inaccurate, are they?

Turn the dial until the temperature is right, then remove the dial knob and place it back on in the correct position. :)

These cheap bimetal regulators are guesswork. Buy yourself something decent with a digital display. The wall temperature should not affect the regulator, unless it has cooled down.

The scaling on the controller corresponds to about 5°C steps (i.e.: 1: 5°C / 2: 10°C ... up to 6: 30°C). so at level 3 it should be about 15°C, but the room is 22°C

One of the biggest misinterpretations with these things is: The scaling would be linear.