An explosion occurred on a gas-powered, 20.88-MW boiler operating by means of a remote monitoring system. Following the detection of an operating defect on the generator burner and its safety mechanism, an on-call technician entered the boiler room to perform verification work. The mandatory control devices, which were inoperable, made it impossible to determine the exact cause of the malfunction. The technician nonetheless reset the automated restart sequence; the explosion happened 30 sec after the pre-sweeping function had begun (air injection into the firebox). The investigation indicated the presence of a foreign body (metal and calamine particles) in both the gas filter and solenoid valves on the gas-powered boiler feed lines, with an imprint of the flap gate of the 1st valve (due to a leak?), as well as significant head losses on the pipeline exposed to the open air (22 m long, with twelve 90° elbows). These anomalies seem to have enabled gas to flow into the generator for 30 min following implementation of burner safety measures. The attempted restart by injecting air into the firebox served to reach the upper flammability limit, in turn causing the explosion to occur within the combustion chamber.