BoilerFaultCodesViessmann F1 Fault Code
The Viessmann F1 fault code means: your boiler has shut down because it detected that the exhaust gases have become too hot, which is a safety feature to prevent damage or dangerous operation.. It appears on 9 Viessmann models in our database.
Technical description: Burner in fault state - Flue gas temperature limiter has responded
What causes the Viessmann F1 fault?
This fault occurs when the internal safety sensors detect that the exhaust gases leaving the unit are exceeding safe temperature limits, triggering an immediate shutdown to protect the internal components. The most common reasons are a build-up of limescale or debris inside the heat exchanger that prevents heat from being transferred to the water, or a fault with the temperature sensor itself. It can also be caused by the burner not firing correctly, leading to excessive heat buildup within the casing.
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 F1 fault code
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Source
Viessmann F1 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