<p>The Earth’s core–mantle boundary hosts structures and processes that affect our planet’s thermal evolution. Spatial and temporal changes in core–mantle boundary heat flux influence core dynamics and its associated geodynamo. These variations, in turn, are controlled by details of mantle dynamics and may be affected by lowermost mantle structures, in particular large low-shear-wave-velocity provinces, which are commonly interpreted as reservoirs of hot, chemically differentiated material. Here we perform simulations of mantle thermochemical convection that account for changes in thermal conductivity with temperature and for excess heating in piles of dense material, modelling large low-shear-wave-velocity provinces. We show that beneath these piles, heat flux can be locally negative, that is, heat flows to the core. In addition, heat flux remains lower than the adiabatic core heat flux throughout the piles base, while slab arrival at the core–mantle boundary triggers high heat flux spikes, increasing lateral heat flux heterogeneity. Our findings support the hypothesis that regional stratification occurs at the top of the core, reconciling present-day geomagnetic and seismic observations in this region. At timescales of 100 Myr, locally negative heat flux may explain the onset and termination of long periods without geomagnetic field polarity reversals known as superchrons.</p>