I have radiator heat in my home. Black water is draining from the overflow, and no water is in my radiators. The water doesn't smell. What's next?

Hi VLewis4. By overflow, do you mean pressure relief valve? If so, you will need to shut the power and incoming water to the boiler off. Now, pressure reliefs blow off for a couple of different reasons. The pressure reducing valve (makeup water valve) may be faulty, allowing too much pressure into the system, or the expansion tank may be bad(waterlogged) , or the pressure relief valve may just be faulty. Either way, you will need to watch and see what the pressure and temperature on the boiler is running at to figure out what exactly is happening.