How do the heating and sanitary hot water circuits function?

Heating and Sanitary Water: The boiler provides the hot water for the heating circuit continuously and as required. When sanitary water is required, hot water to the heating circuit is temporarily cut-off and sanitary hot water is provided by mean of a three-way valve and a secondary heat exchanger Only Sanitary Water: similar to the function of an instant water heater, the boiler only provides instant and continuous hot water as required, returning to a standby mode when the hot water tap(s) are closed.