At what point in a hot water heating system does the pressure remain unchanged, regardless of circulator operation?

The pressure remains unchanged at the connection point of the compression tank in a hot water heating system because this point serves as the reference for the system's pressure. The compression tank, or expansion tank, acts to absorb changes in water volume due to temperature fluctuations, thereby stabilizing the pressure in the heating system.

When water is heated, it expands, and the compression tank accommodates this expansion by allowing excess water to enter it, which prevents substantial increases in pressure. Since the compressive gas in the tank maintains equilibrium with the system pressure, fluctuations caused by the operation of the circulator pump or changes in water temperature do not directly affect the pressure at the connection point.

This is why maintaining the correct pressure at this point is critical for the safety and efficiency of the system. The other points in the system, such as the highest point, boiler exit, or circulator pump, may experience variations in pressure due to both water movement and changes in temperature, thus making them unsuitable as reference points for pressure stability.