How do you add water to sealed heating system?

To add water to a sealed heating system, locate the filling loop, usually a flexible hose connecting the system to the mains water supply. Open the valves on the filling loop to allow water to flow into the system while monitoring the pressure gauge, ensuring it reaches the recommended level (typically 1-1.5 bar). Once the desired pressure is achieved, close the valves and check for any leaks. Finally, bleed any radiators if needed to release trapped air.