  We study three-terminal thermoelectric transport in a two-dimensional Quantum
Point Contact (QPC) connected to left and right electronic reservoirs, as well
as a third one represented by a scanning probe tip. The latter acts as a
voltage probe exchanging heat with the system but no charges on average. The
thermoelectric coefficients are calculated numerically within the
Landauer-B\"uttiker formalism in the low-temperature and linear response
regimes. We find tip-induced oscillations of the local and non-local
thermopowers and study their dependence on the QPC opening. If the latter is
tuned on a conductance plateau, the system behaves as a perfect thermoelectric
diode: for some tip positions the charge current through the QPC, driven by a
local Seebeck effect, can flow in one direction only.
