Low Information
A3:-9 to A3:15 on Viessmann Vitodens 300-W

Your boiler is automatically managing its internal pump to protect the system from freezing based on the outdoor temperature.

Monitor it

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

Outside temperature below 1°C: Heating circuit pump ON; Outside temperature above 3°C: Heating circuit pump OFF

What causes this fault?

This code appears when the outdoor temperature sensor detects that the air outside has dropped to near freezing levels. The boiler responds by automatically activating its internal pump to keep water moving through your pipes, which prevents them from freezing and potentially bursting. It is a built-in safety feature rather than a mechanical failure.

This notification will only appear during the colder winter months when external temperatures drop below 1°C.

DIY fix possible

Check that your outdoor temperature sensor is not covered by snow or debrisMonitor the boiler display to see if the message clears as the weather warms upNo action is required as this is an automated safety function

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