BoilerFaultCodesViessmann E03 Fault Code
The Viessmann E03 fault code means: your boiler has shut down because a safety sensor detected that the exhaust gases are too hot or are not escaping correctly.. It appears on 1 Viessmann model in our database.
Technical description: Burner does not start. Flue gas limiter has tripped. (Reset required: Turn control knob 'Reset' to the right until 'CL' appears, then turn back).
What causes the Viessmann E03 fault?
This fault occurs when a safety sensor detects that the gases produced by the burner are reaching dangerously high temperatures before they can exit the flue. The most common reasons are a build-up of debris or limescale inside the heat exchanger, which prevents heat from being transferred to your water, or a physical blockage within the flue pipe itself.
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 E03 fault code
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Source
Viessmann E03 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