This data contains raw electrical resistivity tomography (ERT) measurements made at the UKGEOS (United Kingdom Geoenergy Observatories) site at Thornton science park in Cheshire, as well as associated metadata, during February 2025. The measurements in this case were made in support of a 3-day closed loop heat injection test starting on the 10th of February 2025. During the test approx. 24kW of heat was equally distributed between 4 observatory heat exchanger boreholes via a circulating heat exchange fluid. This resulted in the fluid delivery temperature increasing from 12 to 27C. The ERT data was collected from 12 boreholes instrumented with ERT electrodes at 1m intervals from 12 to 96 m below the ground surface to facilitate down and cross- hole imaging with electrical currents (1008 electrodes in total). The electrodes are connected to a geoelectrical monitoring system comprising two PRIME servers (1 and 2) which are installed at the site indefinitely. The PRIME instrument is bespoke developed by the British Geological Survey (BGS) for long term geoelectrical monitoring applications, in this case the purpose of the data is to study how the electrical resistivity of the ground responds to temperature changes and other hydrogeological processes. Metadata includes the position of the electrodes within the subsurface, furthermore, finite element meshes are included to aid the user in processing this data. There is a readme (text) file provided with this data that describes its formatting and usage. This data is managed by BGS.