The evolution of non-stationary boundary layers under monotonous heating to a given temperature of the outer surface of one of the walls of a vertical liquid layer is numerically studied. The finite element method is used to solve a system of equations for unsteady thermogravitation convection in the Boussinesq approximation in terms of vortex, stream function, and temperature. The process of formation of non-stationary boundary layers on the heated wall is studied depending on the layer height. In a two-dimensional conjugate problem statement, distributions of non-stationary temperature and velocity fields in a liquid with a Prandtl number of 10 are obtained. Distributions of non-stationary temperature fields in mirror glass walls and temperature gradients on the walls are obtained as well. The calculations are made for the Rayleigh number equal to 106.