I meant free in the natural sense, as in, by using geothermal energy you are not creating any more heat than would have been naturally released anyway -- you're just re-routing and extending the pathway for the same exact amount of heat to be released and getting some work done in the process.
As such, in some sense, with geothermal energy there is no notion of "wasted" power as far as the environment goes. Even if you leave your heaters on unnecessarily, you're just letting the same heat out from your living room instead of letting the same amount of heat escape directly from a fumarole. The heat will have been released either way, and whether you leave your heater on or not only changes where the heat gets released from.
Whereas if you were using, say, nuclear power, leaving your heaters on means that you are wasting nuclear fuel and generating heat that wouldn't have been released had you turned your heaters off.
Also: Geothermal is not free, only the fuel is free. The cost of every electron has to account for the cost of building the plant.