What does a 'circulation pump' do in hot water systems?

A circulation pump plays a critical role in hot water systems by facilitating the efficient movement of hot water through the piping system. Its primary function is to ensure that hot water is continuously circulated, reducing wait times for hot water at fixtures such as taps and showers. This not only improves user convenience but also enhances the overall energy efficiency of the system by minimizing heat loss.

By maintaining a steady flow of hot water, the circulation pump helps to keep the water at the desired temperature and prevents stagnation within the pipes. This is particularly important in large or complex piping systems where hot water may take longer to reach fixtures if it were relying solely on gravity or natural convection.

In contrast, the other options describe functions that do not align with the role of a circulation pump. For example, cooling down hot water or pumping cold water into the system would not be characteristic of a circulation pump's function, as its purpose is to move hot water, not manage temperature by introducing cooler water. Additionally, filtering impurities is associated with water treatment processes, which involve separate systems or equipment specifically designed for that purpose.