BoilerFaultCodesViessmann 79:0 Fault Code
Also written as 790 — same fault.
The Viessmann 79:0 fault code means: your boiler's internal control panel is having a communication error and is struggling to coordinate with other linked components in the system.. It appears on 5 Viessmann models in our database.
Technical description: Control unit is not fault manager
What causes the Viessmann 79:0 fault?
This fault occurs when the main brain of the boiler loses its ability to lead the communication between different internal electronic parts. It is usually caused by a physical break in the wiring connections or a software glitch within the circuit board that prevents it from acting as the 'central manager' for the system.
DIY fix possible
Locate the main power switch for the boiler and turn it off.Wait for approximately 60 seconds.Turn the power back on and press the 'Reset' button on the front control panel.
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Gas Safe Register →Viessmann models that show the 79:0 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 79:0 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