Heat pumps (HPs) are seen as an increasingly important technology able to contribute significantly towards the decarbonisation of the domestic stock in the UK. However, there appears to be a performance gap between predicted and real-life HP performance. This is partly attributed to incorrect assumptions about how they are used in practice, with several studies highlighting the need to include the HP’s interaction with users when examining their performance. This study examines the role of user behaviour and how performance could be improved from a systems perspective. A sample of 21 case studies was selected from 700 domestic HPs monitored across the UK via the government’s Renewable Heat Premium Payment Scheme for the collection of qualitative and quantitative socio-technical data. The application of systems thinking facilitated the identification of the underlying complex interactions between the HP system and its users. The systems analysis revealed that: (a) HP performance relies on an extensive network of complex socio-technical system interactions, many of which relate to behavioural patterns and (b) enabling feedback processes, e.g. through real-time system status indicators and summary displays, can have a significant impact on user behaviour. Feedback processes can also facilitate the timely identification of technical issues and actions that are likely to be detrimental to the system’s efficiency. The study enabled a deeper perspective on performance influencers relating to behavioural patterns and achieved new insights into the requirements for well-performing HPs. These findings have important implications for policy makers, installers and manufacturers of HP systems and their users.