JPH0243985B

PURPOSE:To realize the optimum control of residual hot water with no hot-water shortage and over-heating of hot water by a method wherein the amount of daily residual hot water in a hot water storage tank is memorized and the heating temperature is adjusted once a day and once per unit number of days. CONSTITUTION:The amount of residual hot water on the day is detected by a detecting means (a) for the amount of residual hot water. When the detected amount exceeds the optimum marginal amount X of residual hot water, the detected amount is read-in as one day and at the same time the amount of residual hot water is memorized by a memorizing means (b). In the first unit number of days T1, because the amounts of residual hot water on all the days exceed three times X, the heating-up temperature of the set heating-up temperature lowered by 2alpha deg.C is employed as the heating-up temperature for the following unit number of days T2. In the third unit number of days T3, because the amounts of residual hot water on the days except the (2Y+1)th day and (2Y+4)th day exceed X but are below 2X, the heating-up temperature (85-3alpha) deg.C for the third unit number of days T4 is employed as the heating-up temperature for the following fourth unit number of days T4. In the fourth unit number of days T4, because the amount of residual hot water becomes below X on the (3Y+2)th day, the set heating temperature for the next day is raised by alpha deg.C and the next day is started as the first day in the fifth unit number of days.