BoilerFaultCodesViessmann E04 Fault Code
The Viessmann E04 fault code means: your boiler has detected a flame when there shouldn't be one, which stops it from starting up for safety reasons.. It appears on 1 Viessmann model in our database.
Technical description: Burner does not start. Flame signal is present at burner start-up.
What causes the Viessmann E04 fault?
This fault occurs when the boiler's internal sensors detect a flame or electrical current before the ignition sequence has even begun. The most common cause is a contaminated ionisation electrode sending a false signal, or a fault within the control board incorrectly reading a flame that isn't actually there.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Viessmann models that show the E04 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann E04 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