Air source heat pump water heaters (ASHPWH) fail during service, due to the leakage of the micro-channel condensers. Failure analysis of the condenser was carried out through a series of characterization methods, including energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). Results reveal that the failure of these condensers results from the corrosion of aluminium alloy in acidic aqueous medium, which is constructed by external introduced water and the decomposition products of refrigerant during service. Additionally, the deterioration of refrigeration oil, the abnormal operation of compressor, and the internal defects of condensers also contribute to the failure of the condensers. Finally, a series of countermeasures are proposed for avoiding the corrosion failure of such condensers.