BoilerFaultCodesViessmann E9 Fault Code
The Viessmann E9 fault code means: your boiler has detected an issue while checking its internal systems and has locked itself out to prevent unsafe operation.. It appears on 1 Viessmann model in our database.
Technical description: Burner in a fault state, The ionisation current lies outside the permissible range during calibration
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 E9 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann E9 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 7 July 2026