BoilerFaultCodesViessmann 56:1 Fault Code
Also written as 561 — same fault.
The Viessmann 56:1 fault code means: your boiler's hot water sensor is reporting an unusually high temperature range, which may prevent your hot water from heating correctly.. It appears on 5 Viessmann models in our database.
Technical description: DHW temperature adjustable from 10 to 95°C (only for gas fired boilers). Observe the max. permissible DHW temperature
What causes the Viessmann 56:1 fault?
This fault occurs when the sensor responsible for monitoring your hot water temperature starts sending irregular or 'out of range' signals to the boiler's internal computer. The most common reason is that the sensor has developed an electrical fault or the internal wiring has become slightly corroded, preventing the boiler from knowing exactly how hot your water is. Because the boiler cannot safely verify the temperature, it may restrict hot water production as a precaution.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Viessmann models that show the 56:1 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 56:1 fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026