Warm spots are often caused by a hot water line that’s close to the surface of a concrete slab. Floor joists rest on top of slabs, so flooring materials also rest on those warm spots. Floorboards and carpets will slowly begin to curl up at the edges as they expand with heat from these warm spots. Many times, hot spots on your floor indicate a burst water line or slab leak. More on slab leaks in this article here.