radiant thermal heating is awesome when you have it, and it's working trouble-free. But it's not without its drawbacks.

You have to keep it running through winters, or drain it if it goes dormant, just like a sprinkler system, or it'll freeze and spring leaks. Nice, even heat in winters when you run it, but problematic, especially in a sale, because most people don't know how to care for or run subfloor thermal radiant heat systems.