Viessmann Vitodens 050: Economical Heating in 33.04 sqm Studio Apartment with E200 Thermostat

Hello dear users.
I am asking you for a request because this is my first contact with this type of device.
We rented a studio apartment 33.04 sq m with fiancée. The source of heating in this apartment is a Viessmann Vitodens 050 plus condensing furnace with a control unit with a Viessmann E200 thermostat. There are three radiators in the whole apartment, two in the main room and a third in the bathroom. Regarding this, I have a few issues that bother me, I hope there will be some good person who will help to outline the topic a little:
At this point, we have set 40 degrees for heating water and 60 for heating the house. On the control unit we have constantly set 20 degrees on the room because we have the temperature that suits us. How would you recommend that the gas consumption is the smallest? Because in general we often have to go out for the whole day and come back in the evening. Is it better to reduce the temperature on the unit to 19? Once I tried it all day, the flat did not even get cold. At this point, we moved in 3, considering the preheating of the apartment from 14 to 20 degrees, and hot water, we used 100m3 of gas. How do you think, is it a lot or not? Because I do not know what to think about it. How to program it so that it will be as small as possible? Now I have reduced the stove to 50 degrees, I have the impression that the stove more often turns on and uses more. Any help?
Thank you in advance for your help
greetings

Kamil

You must remember that if it is a condensation furnace, its efficiency grows at lower temperatures. It is best to modulate at low revolutions with a maximum temperature of 55 degrees.

Poki all the time worked on 60, radiators set to 5. I noticed that as this week I changed to 50, then I have a feeling like more often zasaczal, more warmed up, and after the meter I have the illusion as if he was collecting more. With recent frosts of -25, eg one day / night cycle, he collected around 5-6 m3 of gas.

The most important thing is that the stove controls its operation according to the heating curve, trying to work at the lowest speed.
Does a colleague have an external temperature sensor?

I honestly do not know, I suspect that it does not, because this Viessmann E200 control unit works according to the room temperature. The other thing is that it is a studio, one large room and bathroom, so that there is no temperature difference, we leave the bathroom open.

In general, the building was built December 2015 and there is a partanna from the massacre, firstly the grille in the bathroom on a gravitational basis, should draw the air out of the room and circulate, when blowing the intruder into the bathroom, so we had to sew a rag because it quickly wyladzalo.

The second thing is that the flat is too tight, there is no circulation, one vent on the window frame is near the stove, but still the water condenses there and in the frost -25 we had icicles in the room. And if there is no cyrjulation, the window sweats, and there are water stains on the windowsill, and like at night it sometimes even drips on the panels.