BoilerFaultCodesViessmann E05 Fault Code
The Viessmann E05 fault code means: your boiler is unable to start because it cannot confirm that the fan is moving air safely through the system.. It appears on 1 Viessmann model in our database.
Technical description: Burner does not start. Air pressure switch is open at burner start.
What causes the Viessmann E05 fault?
This fault occurs when the boiler's internal safety sensor, the air pressure switch, fails to detect the necessary airflow required to start the combustion process. The most common reason is that either the fan isn't spinning fast enough to move air or the small pipes connecting the sensor have become blocked with debris or moisture. Without confirming that harmful exhaust gases can be safely moved out of the flue, the boiler will refuse to ignite as a safety precaution.
This fault can be more common during periods of high wind or stormy weather, as strong gusts can occasionally create back-pressure in the flue that interferes with the air pressure switch readings.
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 E05 fault code
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Source
Viessmann E05 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