Problem
The target temperature does not seem to trigger the system on/off, unless it’s 1º above or below. For example, you set it to 20º (on timer mode), it’s measuring 19.5º, so under the target temp, but the room does not come on.
Solution
There is a +/- 0.5º deadband on the system.
Also you need to consider the rounding of the system.
For example the 19.5º measured with a target of 20º would only come on once the temperature drops below 19.5º if it was on a downwards temperature slope (the room us cooling).
Also, on the screen you would not see the change in temperature if the measured temperature were to drop to 19.4º. So, some times it would be heating at 19.5º and sometimes it will not. In the background it may have dropped to 19.4º but you don't see that because of the rounding of the app.