BoilerFaultCodesYour boiler is currently running in a special service mode used by engineers to test its performance, and it is not actually reporting a fault.
This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.
Technical description: Calibration Mode (Service Function) - the display will alternate between ‘SF’ and the current boiler temperature and both green LEDs will flash
What causes this fault?
This code appears when the service function has been manually activated, usually by an engineer turning a selector switch to the 'test' position. It physically forces the boiler to run at its minimum or maximum power so that gas levels and performance can be measured accurately. It is not caused by a component failure, but rather by the boiler being placed into a specific operational state for maintenance.
This code is most common during the autumn or spring when homeowners typically book their annual boiler service or safety check.
DIY fix possible
Turn the selector switch to the 'Reset' position and hold for at least 5 seconds.Wait for the display to return to a standard temperature reading.If the code persists, turn the power off and back on at the fused spur switch.
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A boiler cover plan would cover faults like SF — no call-out fees, no surprises.
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