A ground source heat pump (GSHP) system harnesses natural heat from underground by pumping water through it. The heat pump then increases the temperature, and the heat is used to provide heating or hot water.
The pump needs electricity to run, but the idea is that it uses less electrical energy than the heat it produces.
The heat pump performs the same role as a boiler does in a central heating system, but it uses ambient heat from the ground rather than burning fuel to generate heat. Unlike an air source heat pump, which takes heat from the air.