Low Warning
9F on Viessmann Vitodens 222-W

Your boiler has lost communication with the solar heating control panel, meaning your solar panels won't be helping to heat your water.

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.

Technical description

Control mode - Solar control unit fault message

What causes this fault?

This fault occurs when the boiler's main brain can no longer talk to the separate control box that manages your solar thermal system. The most common reason is a loose or damaged communication cable between the two units, or an internal electronic failure within the solar module itself.

DIY fix possible

Check if the solar control panel has powerSwitch the boiler off and back on at the fused spur switch to reset the connectionCheck for any loose external cables connecting the solar controller to the boiler if visible and safe

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Related fault codes

9AView →9CView →

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