I have a GE Profile downward draft cooktop range and noticed that when I turn on 2 burners, the intensity of the flame reduces. When I turn on three burners, then all 3 burners although on high setting show simmered flames. The gas plumber has come and checked out the gas pipeline, pressures at the regulators and at the gas entry point- they are all fine. But I am not sure how to resolve the issue.

Can someone help me? Could it be that there is some blockage in the range? Does anyone know how to clean the range orifice or such? Please help. Its a nightmare cooking.