Low
9F on Viessmann Vitodens 300-W

Your boiler has lost communication with the solar heating system or has detected a fault within the solar control unit.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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.

What the manual says

Manufacturer manual

Control mode: Solar control unit fault message

From this model's manual
Verified against the Viessmann Vitodens 200 W installation & service manual, page 94.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

DIY fix possible

Locate the solar control unit and check for any obvious error messages on its specific displayCheck if the solar pump station is plugged in and the power switch is turned onPerform a 'Soft Reset' by turning the boiler off and back on at the main fused spur

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Related fault codes

9AView →9BView →

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