After running for a few hours (from a clean build), I have the following:
2021-05-19 16:15:01 DEBUG (MainThread) [homeassistant.core] Bus:Handling <Event state_changed[L]: entity_id=climate.controller, old_state=<state climate.controller=heat; hvac_modes=['heat', 'off', 'auto'], min_temp=None, max_temp=None, preset_modes=['none', 'away', 'custom', 'home', 'eco'], current_temperature=21.0, temperature=5.0, hvac_action=idle, preset_mode=eco, heat_demand=0.0, heat_demands=FC=0.0, relay_demands=FA=0.0, F9=0.0, FC=0.0, system_mode=system_mode=eco_boost, until=None, tpi_params=cycle_rate=6, min_on_time=5.0, min_off_time=0.0, proportional_band_width=None, friendly_name=Controller, supported_features=17 @ 2021-05-19T13:51:16.678787+01:00>, new_state=<state climate.controller=heat; hvac_modes=['heat', 'off', 'auto'], min_temp=None, max_temp=None, preset_modes=['none', 'away', 'custom', 'home', 'eco'], current_temperature=21.1, temperature=5.0, hvac_action=idle, preset_mode=eco, heat_demand=0.0, heat_demands=FC=0.0, relay_demands=FA=0.0, F9=0.0, FC=0.0, system_mode=system_mode=eco_boost, until=None, tpi_params=cycle_rate=6, min_on_time=5.0, min_off_time=0.0, proportional_band_width=None, friendly_name=Controller, supported_features=17 @ 2021-05-19T13:51:16.678787+01:00>>
It includes:
... new_state=... heat_demand=0.0 ...
[EDIT] Oh! Hang on…