A backflow preventer used in a boiler system should be located in the:

In a boiler system, the purpose of a backflow preventer is to ensure that water cannot flow backward into the supply line, which could potentially contaminate the water supply. Placing the backflow preventer in the return line close to the boiler is crucial because it helps protect the water supply from any contaminants that may be present in the boiler or the return water.

When installed in this location, the backflow preventer helps to ensure that the system operates safely and efficiently. It minimizes the risk of backflow, which could lead to dangerous conditions, including equipment damage or cross-contamination of potable water supplies. Furthermore, positioning the device close to the boiler ensures that any pressure fluctuations in the system are effectively managed, and it allows for maintenance access while protecting the integrity of both the boiler and the water supply.

Choosing any other location, such as in the overflow line or in a different section of the piping system, would not provide the same level of protection against backflow issues. These other options could allow for potential contamination pathways that compromise the safety and functionality of the boiler and the water supply.