You should start bleeding radiators on the lowest floor of your house, beginning with the radiator that is furthest away from the boiler. This is because air tends to rise in a closed heating system, and the radiator furthest from the boiler often contains the most trapped air. After completing the lowest floor, work your way up to higher floors.

Bleed your radiators ideally before the heating season begins, typically in autumn, or whenever you notice cold spots, slow heating, or unusual noises from the radiators. Regular bleeding, at least once a year or every few months as preventive maintenance, keeps the heating system efficient.