Ground source heat pumps (GSHPs) and district heating (DH) are two common systems used for space heating and domestic hot water in Swedish buildings. They are often considered competitors; however, both heating cost and environmental impact could be optimised by combining these two systems.This paper explores how, and at what cost, DH return line can recharge the boreholes of a decentralized GSHP system. Using current pricing for high-temperature DH, the combined system results in a 22% higher NPV compared to the reference case. To reach a NPV of zero, the maximum allowable cost of charging would need to be 44 SEK/MWh, which is 14% of the current district heat energy price.