Ground source pumps are a tricky install with multiple facets to consider to get it right e.g. ground loop length and size, pump capacity, water storage (ideally separate heating and hot water). System balancing is key or acceptable COP simply won't be achieved. My figures quoted are total since the system was installed ( 18 months). We used the old pipe work flushed through and put in new rads - underfloor would be more efficient but not realistic in my situation. We also run the pump via solar panels giving even greater savings.
The best thing is the entire costs of equipment and installation are repaid over seven years through the government Renewable Heat Incentive scheme ( I even managed to squeeze the solar panels into the total cost to be repaid 👍) The government has switched its green emphasis away from PV into ground and air source so well worth investigating. Install costs are far higher than conventional heating so without government support most people wouldn't consider the move.