Low Warning
9A on Viessmann Vitodens 050-W

Your boiler has lost communication with the temperature sensor that monitors the outdoor solar panels or the system collector, meaning it cannot accurately manage heat levels for those components.

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: Collector temperature sensor lead break

What causes this fault?

This fault occurs when the boiler can no longer receive data from the sensor attached to your solar heating panels. The most common reason is a physical break in the cabling or a failed electrical component within the sensor itself, often caused by long-term exposure to the elements or loose connections. Since the boiler cannot see how hot the solar panels are, it stops using them to heat your water as a safety precaution.

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

9BView →9CView →

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