The exact temperature setting for a combi boiler is not set in stone, though there are some generally accepted guidelines for efficient operation and heating performance.
For a modern combi boiler, the radiator heating temperature should be set for a flow temperature of between 60 and 70°C. Any higher than this and the boiler won’t enter condensing mode and be at its optimum efficiency and performance. In spring and Autumn months, consider reducing the boiler’s radiator temperature further - to around 50 or 55°C, as this will provide additional efficiency at the cost of heating performance. As an additional note, this temperature setting refers to the temperature of the water inside the radiators whilst heating your home. Depending on your home, for example if you have done some fabric improvements since the original heating system was installed, it may be possible to leave the setting at between 50 to 55°C even during winter. The lower the heating flow temperature, the more efficient the heating system - lowering your gas consumption and consequently running costs.
Meanwhile, we recommend the hot water temperature to be set at around 50°C. Anything over 45°C at the point of use (tap or shower) can cause scalding so would need to be mixed down with the cold water. This setting should again provide an ideal balance of heating performance, comfort and efficiency for the majority of homes.