A pressure surge, most likely due to an explosion within the combustion chamber, tore off a large portion of the outer lining on a 6.9-MW boiler running on municipal gas in automated mode. The boiler room was protected by cutting the gas supply via the external valve. The fire department was called but did not have to intervene given the absence of fire and no injuries. Three days prior, following replacement of the burner, all safety tests were successfully conducted. The boiler was also being used as an auxiliary to the cogeneration system. The day before the accident, the gas-fired burner was protected following a pressure drop. The sector foreman requested that the cogeneration facility be shut down and that the boiler be allowed to operate on its own. The boiler was restarted around midnight; 2½ hours later, it had to be secured following a problem on the burner. The explosion occurred when power was restored 2 hours after that. An investigation was conducted to determine the exact causes.