In this paper, both switches open/short circuit faults diagnosis and a fault tolerant diagram of a photovoltaic (PV) fed Three-Level Boost DC-DC Converter (TLBDC) are addressed. Diodes voltages are used to detect open or short circuit faults. These voltages are also used to ensure voltage balance control of the TLBDC. Hence, the number of sensors would be the same as the number of sensors used in a conventional TLBDC controller scheme. The proposed method identifies and locates the faulty switch easily. The TLBDC is reconfigured where the ensured input power and output voltage remain unchanged. This is achieved by adding only one extra power switch to the TLBDC topology. Simulation and experimental results confirm the effectiveness of the proposed fault diagnosis method and the TLBDC fault tolerant scheme.