What is the function of a run-around pump on some hot water boilers?

The function of a run-around pump in hot water boilers primarily revolves around enhancing the efficiency of heat transfer. This pump circulates water through a heat exchanger, allowing water that has been heated by the boiler to flow back to a separate location, often another part of the system or a secondary loop, before returning to the boiler. By doing this, the run-around pump effectively increases circulation within the system and helps to bring the hot water boiler up to operating temperature more quickly.

As water circulates effectively, it assists in maintaining the temperature consistency throughout the system. This not only speeds up the heating process but also contributes to a more uniform temperature distribution, reducing heat loss and improving overall efficiency. The design and operation of a run-around system often result in energy savings and improved performance, particularly in larger installations where heat needs to be distributed over considerable distances.

Other choices do not capture the primary role of the run-around pump: while keeping discharge and return lines at the same pressure might be a function of other components in a system, increasing discharge pressure refers more to pumps specifically designed for that purpose, and "none of the answers given" does not apply as there is a clearly defined function for the run-around pump.