BoilerFaultCodesViessmann E12 Fault Code
The Viessmann E12 fault code means: your boiler's main control computer and the front display screen have stopped talking to each other, meaning the unit cannot function.. It appears on 1 Viessmann model in our database.
Technical description: Control unit fault. Communication error with the display.
What causes the Viessmann E12 fault?
This fault occurs when the internal communication link between the boiler's main brain and the front control panel is broken. It is usually caused by a loose internal connection cable, a short circuit on one of the circuit boards, or moisture ingress affecting the sensitive electronics.
DIY fix possible
Turn the boiler power off at the fused spur switch (the wall switch).Wait for 60 seconds.Turn the power back on and see if the display restarts normally.
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Gas Safe Register →Viessmann models that show the E12 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann E12 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