CFD simulation of the combustion process in a 120MW gas fired industrial boiler has been performed, with focus on the flow pattern and temperature distribution at the reheater section in the furnace. The modeling was done using general-purpose CFD software, CFD-ACE+ developed by CFD Research Corporation. The effect of imbalance burner pressure is simulated by varying the mass flow rate of fuel (natural gas) injected at each burner. The simulation result shows good qualitative agreement with practical observation. The flow in the furnace is highly swirling with intense mixing and follows a helical pattern in an anticlockwise direction. Temperature distribution prior to entry to the reheater is significantly higher on the right side of the reheater. As a conclusion, the imbalance nozzles pressure creates uneven mass flow rate of air and fuel, which results in asymmetric flow pattern and temperature distribution at the reheater section.