Electron heating due to nonlinear Landau damping of electrostatic waves in an electron beam-plasma system is studied theoretically. The fast and slow space charge waves of an electron beam and the Trivelpiece-Gould modes interact nonlinearly with plasma or beam electrons and cause an effective electron heating and a beam relaxation which leads to a saturation of electron heating. For nonlinear interaction with plasma electrons, the virtual (beat) wave produced by the two electrostatic waves can heat plasma electrons by its electron cyclotron damping. On the other hand, for nonlinear interaction with beam electrons, the Trivelpiece-Gould mode enhanced by nonlinear Landau damping can heat plasma electrons by its electron Landau damping. For both cases, the conservation of total energy flux and the existence of the energy transport are proved quantitatively.