Lava planet

Perhaps if it was in a position similar to Mercury and had the very large heavy elements and appropriate tectonic shifts. Venus could also serve as a slight example of this due to numerous volcanic activity. But if a planet was a complete ball of lava it would have to be very close to the sun or part of a runaway greenhouse effect. It would have to be hot enough for the lava to never cool. Even Hadean Earth had a lava like environment teeming with volcanoes and rivers of lava. But due to gases and other parts of cooling this condition abated. With that, a third variable our lava planet could need is a non equilibrium or non-cooling type atmosphere so again the lava can keep in its liquid form. A fourth item to consider, the core and mantle of the planet. If still hot and active enough then the internal temperature of the planet can contribute to the lava flow. The fifth item is a sort of cycle with the lava flows so a more violent but open tectonic system is needed.