This is a technical status message indicating the boiler is adjusting its fan speed settings and is not usually a hardware 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: Offset for minimum speed
What causes this fault?
This message occurs when the boiler's internal computer is calibrating the fan to ensure it spins at the correct minimum speed for safe combustion. It is a natural part of the boiler's self-check process to compensate for minor fluctuations in air pressure or electrical signals. In most cases, it is simply the boiler 'fine-tuning' itself and will disappear once the adjustment is complete.
DIY fix possible
Check if the display returns to a standard temperature reading after a few minutesPerform a simple reset by pressing the 'Flame' or 'R' buttonMonitor the boiler to see if the code disappears during normal operation
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