HOT WATER SUPPLIER

A hot water supplier includes a combustion unit including multiple combustion stages; a combustion fan supplying combustion air; a fuel supply unit supplying fuel; a heat exchange unit; a water supply unit supplying hot water to heat exchange unit; a hot water tapping unit discharging hot water heated in heat exchange unit by using combustion heat obtained by burning fuel in combustion unit; and a control unit controlling heating operation. When reheating operation is allowed in which hot water from hot water tapping unit is returned to water supply unit and reheated by heat exchange unit, control unit stores heating time using only a combustion stage having minimum combustion capacity during reheating operation as time data. If this time data tends to increase over time, deterioration progress of a heat retaining material covering a hot water pipe to which hot water is supplied from hot water tapping unit is determined.