What exactly does your condition with externalWallHeatFluxTemperature look like? Did you use the heat flux mode? If you did, you can take your result and use (or whatever equivalent you have in the openfoam version you are using, for the foundation v11 I use this): - foamPostProcess -region {your solid region} -solver solid -time {your final time} -func wallHeatFlux To see whether or not the heat flux 38700 W/m² yields the expected power of 200 W on that patch. If the power transfer is correct, then it could be an issue with your physical properties, or perhaps you've encountered some sort of bug.