A malfunction detection device for a hot water supplier has a tank temperature detection thermistor for detecting a hot water temperature of a hot water storage tank and is configured such that when the detected hot water temperature of the hot water storage tank is a reference temperature or higher, a relay provided at a tank printed circuit board stops power supply from a tank unit to a heat pump unit. A heat pump shutdown command is a standby power saving command for saving a standby power of the heat pump unit.