Where should the primary circulator be located in a plumbing system?

The primary circulator in a plumbing system is ideally positioned downstream of the expansion tank. This placement allows the circulator to effectively manage the flow of water throughout the system, ensuring that it can respond appropriately to changes in water pressure and temperature.

By locating the circulator downstream, it is positioned in a way that takes advantage of the pressure equalization provided by the expansion tank. This configuration helps in maintaining a consistent circulation of water, improving both efficiency and performance. It also ensures that any thermal expansions occurring in the system can be accommodated effectively without putting excessive strain on the circulator or other components.

Considering the other options, placing the circulator upstream of the expansion tank could interfere with the necessary pressure management and cushioning effect that the tank provides. Positioning it adjacent to the water heater would not optimize the system's performance as it may not effectively circulate heated water throughout the entire system. Lastly, situating the circulator at the main water supply line is not practical since it may not provide the necessary flow dynamics required for effective circulation within the heating system.