Abstract: When a hot water supply operation is started, a single mode is used in which hot water is output only from a second hot water supply circuit of a water heater, by cut-off of a flow path in a first hot water supply circuit of a space-heating water heater by a cut-off mechanism. When a load imposed by hot water supply by the second hot water supply circuit increases during the hot water supply operation in the single mode, the cut-off mechanism is opened to start hot water output from the first hot water supply circuit and a hot water supply operation in a parallel mode is performed in which hot water is output from both of the first hot water supply circuit and the second hot water supply circuit.

Abstract: When a hot water supply operation is started, a single mode is used in which hot water is output only from a second hot water supply circuit of a water heater, by cut-off of a flow path in a first hot water supply circuit of a space-heating water heater by a cut-off mechanism. When a load imposed by hot water supply by the second hot water supply circuit increases during the hot water supply operation in the single mode, the cut-off mechanism is opened to start hot water output from the first hot water supply circuit and a hot water supply operation in a parallel mode is performed in which hot water is output from both of the first hot water supply circuit and the second hot water supply circuit.

Abstract: In a suction fan type combustion apparatus, when an air supply/exhaust path of a combustion and heating unit is clogged, a combustion fan has a degraded fan current for the same fan rotation speed. Furthermore, the suction fan type configuration has the combustion and heating unit's internal pressure reduced as the combustion fan rotates faster. A combustion burner supplies fuel gas with a pressure applied thereto, which is regulated by a gas proportional valve. A degree of opening of the gas proportional valve is corrected in a direction allowing the pressure to be reduced, in accordance with a rate of degradation of a fan current relative to a reference current following a reference current characteristic. This control for correction is done with the fan current degradation rate smoothed (or low-pass filtered) in a time base direction.

Abstract: By a feedback arithmetic operation based on a temperature deviation, an input number is set which corresponds to a requested heat quantity generation, which is a controlled object, to a hot water supply apparatus. The temperature deviation is calculated by correcting a deviation of a tapping temperature with respect to a set hot water temperature with use of a Smith compensation temperature calculated by a Smith compensator for predicting a variation in a tapping temperature prior to an elapse of a dead time corresponding to a detection lag of the tapping temperature. The Smith compensator calculates a Smith compensation temperature to be used in the next control cycle based on the input scale number, the present Smith compensation temperature, and a time constant set in accordance with a flow rate of the hot water supply apparatus.

Abstract: A conversion factor learning unit successively updates a temperature conversion factor by learning a performance ratio of an output heat quantity with respect to an input scale number corresponding to a requested heat quantity generation to a hot water supply apparatus. The temperature conversion factor learned by the conversion factor learning unit is reflected in arithmetic operation of an FF scale number by a feedforward control unit and arithmetic operation of the FB scale number by the feedback control unit. An integral control in the feedback control unit is preferably turned off.

Abstract: In a suction fan type combustion apparatus, when an air supply/exhaust path of a combustion and heating unit is clogged, a combustion fan has a degraded fan current for the same fan rotation speed. Furthermore, the suction fan type configuration has the combustion and heating unit's internal pressure reduced as the combustion fan rotates faster. A combustion burner supplies fuel gas with a pressure applied thereto, which is regulated by a gas proportional valve. A degree of opening of the gas proportional valve is corrected in a direction allowing the pressure to be reduced, in accordance with a rate of degradation of a fan current relative to a reference current following a reference current characteristic. This control for correction is done with the fan current degradation rate smoothed (or low-pass filtered) in a time base direction.

Abstract: A conversion factor learning unit successively updates a temperature conversion factor by learning a performance ratio of an output heat quantity with respect to an input scale number corresponding to a requested heat quantity generation to a hot water supply apparatus. The temperature conversion factor learned by the conversion factor learning unit is reflected in arithmetic operation of an FF scale number by a feedforward control unit and arithmetic operation of the FB scale number by the feedback control unit. An integral control in the feedback control unit is preferably turned off.

Abstract: By a feedback arithmetic operation based on a temperature deviation, an input number is set which corresponds to a requested heat quantity generation, which is a controlled object, to a hot water supply apparatus. The temperature deviation is calculated by correcting a deviation of a tapping temperature with respect to a set hot water temperature with use of a Smith compensation temperature calculated by a Smith compensator for predicting a variation in a tapping temperature prior to an elapse of a dead time corresponding to a detection lag of the tapping temperature. The Smith compensator calculates a Smith compensation temperature to be used in the next control cycle based on the input scale number, the present Smith compensation temperature, and a time constant set in accordance with a flow rate of the hot water supply apparatus.