BoilerFaultCodesViessmann 93 Fault Code
The Viessmann 93 fault code means: your boiler has detected a technical fault with a sensor in your solar heating system, which may affect its ability to heat your water using solar energy.. It appears on 3 Viessmann models in our database.
Technical description: Control mode - Solar: Sensor S3 shorted out
What causes the Viessmann 93 fault?
This fault occurs when the temperature sensor responsible for monitoring your solar hot water cylinder develops a short circuit, preventing the boiler from receiving accurate data. The most common reason is water ingress or heat damage to the sensor probe itself, but it can also be caused by physical damage or a pinch in the electrical cable connecting the sensor to the control unit.
This fault is more common during the summer months when solar thermal systems are under peak thermal stress and high temperatures are most likely to degrade older sensor components.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Viessmann models that show the 93 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 93 fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.
- Viessmann Vitodens 050-W manual (PDF)
- Viessmann Vitodens 100-W WB1A manual (PDF)
- Viessmann Vitodens 222-F manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026