What function does a mixing valve serve in hydronic heating systems?

A mixing valve plays a crucial role in hydronic heating systems by regulating water temperature. It achieves this by mixing hot water from the boiler with cooler return water that has circulated through the heating system. This process ensures that the water supplied to the system is at the optimal temperature for efficient heating.

Maintaining the correct water temperature is vital for the comfort of the end-users and for the overall efficiency of the system. By blending these two sources of water, the mixing valve helps to prevent overheating, reduces the risk of damaging the system components, and enhances energy efficiency by ensuring that less heat is wasted. In contrast, the other options do not accurately describe the primary function of a mixing valve. While controlling boiler pressure, filtering pollutants, and monitoring water levels are important functions in a hydronic system, they do not pertain to the specific role of a mixing valve.