A heat pump is a straight replacement of your current boiler, it heats your home and hot water. It is a device that moves heat from one location (the ‘source’) to another location (the ‘sink’ or ‘heat sink’) using mechanical work.
Most heat pump technology moves heat from a low temperature heat source to a higher temperature heat sink. Common examples are food refrigerators and freezers, air conditioners. Heat pumps can be thought of as a heat engine which is operating in reverse. Most commonly, heat pumps draw heat from the air or from the ground.