Yes, there are disadvantages to geothermal heating. Some of them are: generates waste, location restricted (meaning you cannot use it everywhere), reservoirs require proper management, and high initial cost. In the most extreme cases, it can also cause an earthquake. Geothermal heating has the potential to become a major global energy source; it just requires a bit high upfront cost which is holding it back. Read the full guide for more info on geothermal heating and other eco-friendly heating alternatives.