BoilerFaultCodesViessmann 68 Fault Code
The Viessmann 68 fault code means: your boiler has lost its connection to the sensor that measures the water temperature coming back into the unit, which often results in the system shutting down for safety.. It appears on 3 Viessmann models in our database.
Technical description: Control mode: Return temperature sensor lead break
What causes the Viessmann 68 fault?
This fault occurs when the boiler’s internal computer loses the electrical signal from the sensor that monitors the temperature of the water returning from your radiators. The most common reason is that the sensor itself has developed an internal electrical failure or the thin wires connecting it to the main control board have become loose or damaged. Because the boiler can no longer verify if the water is at a safe temperature, it shuts down as a precautionary measure.
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 68 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 68 fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.
- Viessmann Vitodens 100-W manual (PDF)
- Viessmann Vitodens 100-W B1GA manual (PDF)
- Viessmann Vitodens 100-W WB1A manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026