A device installed on the supply of the boiler and removes air from the system

• A. Flow check
• B. Automatic air vent
• C. Expansion tank
• D. Pressure relief valve

Answer: (B)

Air in a boiler or hydronic heating system can pinball through the pipes, creating cold spots, noise, and reduced efficiency. An automatic air vent placed on the supply side of the boiler is designed to continuously purge that trapped air. As air collects at high points, the vent opens to let the air escape to the outside and then closes again when water reaches the vent, preventing water loss. This function is specifically about removing air automatically, which is why it's the right choice. The other devices serve different purposes: a flow check prevents backflow, an expansion tank absorbs added volume as water heats, and a pressure relief valve protects against overpressure.