Air separators used in hot water heating systems trap the air and direct it to the:

In hot water heating systems, air separators play a crucial role in maintaining the efficiency and safety of the system. Their primary function is to remove trapped air from the water, which can lead to issues such as reduced heating efficiency, noise, and even damage to components of the system.

The correct answer highlights that air separators direct the trapped air to the expansion tank. The expansion tank serves as a vital component of the system; it provides a space for the air to accumulate away from the hot water circuit. By transferring the trapped air to the expansion tank, the system can prevent air pockets from forming in the pipes and heating elements, thereby maintaining a consistent flow and optimal operation.

Other components like the boiler, convector, or pump are not suitable destinations for the trapped air because sending air to these parts could result in operational problems. For example, air in the boiler can lead to poor heat transfer or corrosion, while air in the pump can cause cavitation, potentially damaging the pump. Thus, directing air to the expansion tank is essential for the overall health and performance of hot water heating systems.