What is the purpose of the expansion tank in a hot water boiler system?

The function of the expansion tank in a hot water boiler system is critical for managing the thermal expansion of water as it heats up. As water is heated, it expands, and without a designated expansion space, this increase in volume can lead to excessive pressure within the system. This could potentially cause damage to the boiler or the piping, resulting in leaks or even catastrophic failures.

The expansion tank provides a buffer for this increased volume. It allows for the additional water to move into the tank, thereby accommodating the expansion and maintaining the system's pressure within safe limits. This not only protects the integrity of boiler components but also promotes the overall reliability of the heating system.

The other options, while they may seem relevant, do not accurately describe the primary purpose of the expansion tank. For instance, storing excess water when the system is shut down, enhancing heat exchange efficiency, or ensuring a continuous supply of water during heating do not capture the core function, which focuses primarily on managing the effects of thermal expansion.