Hello Mshaeli19
thanks for reaching out to us here in the forum.
As you are using the CHT.V2 the temperature of the surface will be defined by heat transfer and therefore shouldn’t be set by a boundary condition.
In order to set the heat of the body please assign geometry to a power source.
One point in regards to the setup of your boundary conditions please have a look at this tutorial which in regards to the physics is similar to yours.
Best regards
Sebastian