Junkers Boiler ZWB 24-23: Strange Symbol & Summer Mode Indicator Constantly On - Help Needed

Hello. I have a question I rent a flat and it has the above mentioned boiler. When heating, the symbol pops up as in the video. In addition, the summer mode indicator lights up constantly.

[Film: 7ac1157067] https://filmy.elektroda.pl/28_1509531402.mp4 [/ film: 7ac1157067]

Can anyone help? I am not familiar with these devices. And how to set it best?

Hello,
This symbol means that the boiler works for 15 minutes with the lowest heating power.
However, if it alternately shows the temperature and this sign it means that the siphon filling program is active.
The siphon filling program is activated
in the following cases:
o
Turning on the boiler with the on / off switch
o
The burner has not been used for 28 days.
o
The summer mode will be changed
for winter.

I understand, because that's when the temperature doesn't rise from what I saw. And how best to set it so that it does not take a colossal amount of gas?
The flat has about 57m2, it is an extension at the top of the house, the whole added part is insulated. However, the windows are wooden and the stairs are slightly colder than the small window.

And I still have a question whether the temperature on the stove after turning off the burner should keep or decrease?

Set the minimum heating comfort parameters on the heating controller.
If it is not there, then the boiler regulation remains, but that's the service.

And on the boiler what temperature to set? For example, the room has a temperature of 20 C, on the stove how much should it be, so that it still does not turn on?

At this link you have the boiler instructions: http://en.documents.junkers.com/download/pdf/file/6720864855.pdf