The boiler does not try to reach taeget temperature

[gituletz]

Hello,
I have the Home Assistant Ariston integration in use for a Condensing Genus One gas boiler.
I am setting the desired(target) temperature calling the service:
service: climate.set_temperature
target:
entity_id: climate.ariston
data:
temperature: 23.5

What I have observed is that the boiler never tries to reach the target temperature. It always stays below.
Even stranger is that the climate.ariston history graphs display 3 temperatures (see in the pictures below):
blue: Ariston Heating Target Temperature Current: which varies around 21C
orange: Ariston Heating Target Temperature Heating (tops at 21C)
Ariston Heating Target Temperature target temperature: 23.5C, never reached

Am I setting the right entity with the desired temperature?
The boiler is in Winter preset and the Heat HVAC mode.

If I set the desired temperature on the Ariston net thermostat instead of using HA, the boiler is able to reach the desired temperature shortly.