My radishes this year are almost too hot to eat.
Radishes get hot for a number of reasons.
If they are too old they are hotter, and if they were grown under low fertility or if they got too dry, and their growth was not as fast as it should have been, then they turn hot. All I ever get is strings. Many of the rooting vegetables will not perform as well in heavy soils. Try amending your soil with some compost to make it loose. Be sure to thin your seedlings at an early stage to allow room for growth.