Minnesota Boiler License Practice Exam

What device must be located between a hot water boiler and the expansion tank?

1. A shut-off valve

2. Two temperature controls

3. A low fire limit control

The correct answer is: A shut-off valve

The presence of a shut-off valve between a hot water boiler and the expansion tank is essential for the safe operation and maintenance of the system. This valve allows for the isolation of the boiler from the expansion tank during maintenance or service activities. It helps prevent potential water hammer and ensures that any repairs can be performed without the risk of flooding or water escaping from the system. In contrast, the other devices mentioned—two temperature controls and a low fire limit control—do not serve the same function. Temperature controls are typically implemented to monitor and manage the temperature of the water within the system, while a low fire limit control is designed to prevent the boiler from operating under dangerously low water conditions. However, these devices do not provide the ability to isolate the boiler from the expansion tank, which is critical in maintaining safe and efficient operation. Thus, the necessity of a shut-off valve is fundamental in the setup between a hot water boiler and the expansion tank.