On the 27th the heating system started up for the first time, sometime during the day.
Last year it was on the 21st.
In 2020 it was on the 26th.
It has been colder than usual this time of year, so setting the base temperature lower (19C rather than 20C or 21C) as we did at the start of the year is having an effect. Probably it would have engaged a week earlier otherwise.