A method for controlling a hot water circulation system comprising a heat pump, the hot water circulation system comprising a heat pump (2, 3) comprising: an outdoor unit including a compressor, an outdoor heat-exchanger having a refrigerant pipe, an outdoor heat-exchanger temperature sensing unit to sense a temperature of the refrigerant pipe surface, an expansion part, and an outdoor fan mounted on the compressor, and performing a heat pump refrigerant cycle; an indoor unit including a water-refrigerant heat-exchanger which performs heat exchange between a refrigerant discharged from the compressor and water, water-refrigerant heat-exchanger temperature sensing unit to sense a temperature of water at an outlet side of the water-refrigerant heat-exchanger, a water collection tank in which water passing through the water-refrigerant heat-exchanger is stored, and a water pump which pumps water discharged from the water collection tank; characterised by a hot water circulation unit (4, 5) which receives heat from the water pumped from the water pump to perform hot water supply or heating, the hot water circulation unit including a hot water supply tank in which water supplied from outside of the hot water circulating unit is stored and, an auxiliary heater (35, 42) provided in the water collection tank and hot water supply tank, and wherein the method comprises: sensing a refrigerant temperature of the refrigerant pipe and a temperature of water at the outlet side of the water-refrigerant heat-exchanger; and changing an operation condition of the outdoor unit, including reducing an operating rate of the compressor, reducing a velocity of the outdoor fan and controlling an opening of the expansion part when the refrigerant temperature drops below a defrosting requisite temperature Ta; after changing the operation condition of the outdoor unit or determining that the refrigerant temperature is higher than a defrosting temperature Ta, determining whether the sensed water temperature at the outlet side of the water-refrigerant heat exchanger is below a setting temperature Tb; when the water temperature is below a setting temperature Tb changing an operation condition of at least one of the indoor unit and hot water circulation unit (4, 5), comprising at least one of: selectively operating the auxiliary heater provided in at least one of the water collection tank and hot water supply tank, and reducing an output of the water pump. an outdoor unit including a compressor, an outdoor heat-exchanger having a refrigerant pipe, an outdoor heat-exchanger temperature sensing unit to sense a temperature of the refrigerant pipe surface, an expansion part, and an outdoor fan mounted on the compressor, and performing a heat pump refrigerant cycle; an indoor unit including a water-refrigerant heat-exchanger which performs heat exchange between a refrigerant discharged from the compressor and water, water-refrigerant heat-exchanger temperature sensing unit to sense a temperature of water at an outlet side of the water-refrigerant heat-exchanger, a water collection tank in which water passing through the water-refrigerant heat-exchanger is stored, and a water pump which pumps water discharged from the water collection tank; characterised by a hot water circulation unit (4, 5) which receives heat from the water pumped from the water pump to perform hot water supply or heating, the hot water circulation unit including a hot water supply tank in which water supplied from outside of the hot water circulating unit is stored and, an auxiliary heater (35, 42) provided in the water collection tank and hot water supply tank, and wherein the method comprises: sensing a refrigerant temperature of the refrigerant pipe and a temperature of water at the outlet side of the water-refrigerant heat-exchanger; and changing an operation condition of the outdoor unit, including reducing an operating rate of the compressor, reducing a velocity of the outdoor fan and controlling an opening of the expansion part when the refrigerant temperature drops below a defrosting requisite temperature Ta; sensing a refrigerant temperature of the refrigerant pipe and a temperature of water at the outlet side of the water-refrigerant heat-exchanger; and changing an operation condition of the outdoor unit, including reducing an operating rate of the compressor, reducing a velocity of the outdoor fan and controlling an opening of the expansion part when the refrigerant temperature drops below a defrosting requisite temperature Ta; after changing the operation condition of the outdoor unit or determining that the refrigerant temperature is higher than a defrosting temperature Ta, determining whether the sensed water temperature at the outlet side of the water-refrigerant heat exchanger is below a setting temperature Tb; when the water temperature is below a setting temperature Tb changing an operation condition of at least one of the indoor unit and hot water circulation unit (4, 5), comprising at least one of: selectively operating the auxiliary heater provided in at least one of the water collection tank and hot water supply tank, and reducing an output of the water pump.