What prevents the boiler water from over-pressurizing the condensate receiver?

The correct answer is a check valve because it serves a crucial function in ensuring that water flows in one direction only, preventing backflow into the system. In the context of a boiler and its condensate receiver, the check valve allows condensate to flow from the boiler into the receiver while preventing the water at a higher pressure in the boiler from pushing back into the condensate receiver. This helps to maintain safe operating pressures and avoids potential damage that could occur if the condensate receiver were to become over-pressurized.

Using a strainer, while it does help to keep debris and foreign objects out of the system, does not control pressure or fluid direction like a check valve. A relief valve, on the other hand, is designed to release pressure when it exceeds a certain set point, which is important for overall safety but does not actively prevent over-pressurization in the way that a check valve does. Finally, a flow restrictor limits the flow rate of the fluid but does not prevent pressure issues directly related to the backflow or misdirection of fluid within the system, which is the primary function needed in this scenario.