Fundamentally there are two things every hydronic system you’ll ever design or install “wants” to do — they all want to operate at simultaneous conditions called thermal equilibrium and hydraulic equilibrium. Both conditions represent a balance between energy input and energy release.
Thermal equilibrium means every system seeks to operate where the rate of heat input to the water from the heat source (boiler, heat pump, etc.) is exactly the same as the rate of heat release from the water to the heat emitters. The supply-water temperature and the temperature drop the system stabilizes to are always those necessary to balance these rates of heat flow. In some situations, these temperatures can be significantly higher or lower than what we expect based on control settings.