Boiler repair. I bled the system to remove trapped air, which makes the heating system more efficient. Air bubbles prevent hot water from circulating properly, leading to cold spots on radiators, gurgling noises, and reduced heat output. Bleeding also protects the system from rust and corrosion, as air contains oxygen that can damage the metal components. The system doesn’t have shut-off valves. Had to remove the pump to bleed. The boiler is 20 + years old.