  The effective potential of the order parameter for confinement is calculated
within the Hamiltonian approach to Yang--Mills theory. Compactifying one
spatial dimension and using a background gauge fixing this potential is
obtained by minimizing the energy density for a given background field. Using
Gaussian type trial wave functionals I establish an analytic relation between
the propagators in the background gauge at finite temperature and the
corresponding zero temperature propagators in Coulomb gauge. In the simplest
truncation, neglecting the ghost and using the ultraviolet form of the gluon
energy one recovers the Weiss potential. From the fully non-perturbative
potential (with the ghost included) one extracts a critical temperature of the
deconfinement phase transition of 270 MeV for the gauge group SU(2).
