Water heating apparatus and water heating system

A water heating system comprising:

• a water heating apparatus including a water entry port and a hot water output port;
• a low-temperature water pipe that introduces low-temperature water to the water entry port;
• a high-temperature water pipe that connects the hot water output port and a hot water supply faucet to each other;
• and
• a circulation pump arranged inside or outside the water heating apparatus,
• the water heating apparatus including
• a heating mechanism including a combustion mechanism,
• an inner path,
• in an immediate hot water supply operation mode in which the circulation pump is activated while the hot water supply faucet is closed, the inner path forming an immediate hot water supply circulation path through which fluid passes through the heating mechanism, as being combined with an outer path, the outer path bypassing the hot water supply faucet on outside of the water heating apparatus,
• a first temperature detector that detects a fluid temperature upstream from the heating mechanism in the immediate hot water supply circulation path,
• a second temperature detector that detects a fluid temperature downstream from the heating mechanism in the immediate hot water supply circulation path;
• a flow rate detector that detects a circulation flow rate in the immediate hot water supply circulation path, and
• a controller that controls the heating mechanism and the circulation pump, wherein
• the outer path includes a thermal water stop bypass valve including a path that is closed when a temperature increases,
• the controller includes
• a heat quantity controller that sets, in the immediate hot water supply operation mode, an output heat quantity command value for the combustion mechanism for controlling a temperature detection value detected by the second temperature detector to a set temperature in the immediate hot water supply operation mode, and
• a combustion controller that controls the combustion mechanism in accordance with the output heat quantity command value,
• the output heat quantity command value is set as being restricted within a range from a minimum heat quantity value to a maximum heat quantity value in a combustion state of the combustion mechanism, and
• the combustion controller controls the combustion mechanism in the immediate hot water supply operation mode so as to alternately provide a minimum combustion state and a combustion stop state when the output heat quantity command value is set to the minimum heat quantity value and when the temperature detection value detected by the second temperature detector increases to a control upper limit temperature set to be higher than the set temperature,
• in the minimum combustion state, the combustion mechanism operates in accordance with the minimum heat quantity value.