Flow temperature is the temperature of water leaving the boiler for the radiators. It is different from the room thermostat and, on a combi boiler, different from the domestic hot-water setting.\n\nA lower heating flow temperature can help a condensing boiler operate efficiently, but the home must still warm properly. Insulation, radiator size, weather and system design all affect the right setting.\n\nOnly adjust the heating flow control described in the user manual. Do not reduce stored hot-water cylinder temperatures without professional advice because hot-water hygiene needs different consideration.\n\nMake small changes, observe comfort over several days and return to the previous setting if the home no longer heats adequately. Ask an engineer to review the system if controls are unclear or rooms struggle to reach temperature.\n\nThe linked Energy Saving Trust article explains the distinction between combi and system boilers and the circumstances that affect safe adjustments.