Daily #homeassistant lesson - #heating.
For several months, I regulated the temperature in my office using 2 simple automations: turn the radiator pump on/off.
There is a 'better' way: using #genericthermostat and #scheduler components:

1. Configure a Generic thermostat in your configuration.yaml (https://www.home-assistant.io/integrations/generic_thermostat/)
(you need one temperature sensor and one switch)