The running costs of a heat pump will vary from house type to house type. A well-insulated house built to new building regulation standards will generally be less expensive to run than a gas or oil fired boiler system providing the heating system flow temperatures are kept relatively low, ideally around 40ºC.
A heat pump will be less efficient and more costly to run when generating higher temperatures, either because the house isn’t well insulated, the radiators are insufficiently sized for the lower temperatures or when generating higher temperatures to produce hot water.