BoilerFaultCodesViessmann E15 Fault Code
The Viessmann E15 fault code means: your boiler is struggling to start because it cannot get a correct temperature reading from the sensor located on the outside of your house.. It appears on 1 Viessmann model in our database.
Technical description: Burner does not start. Outside sensor fault (short circuit or lead break).
What causes the Viessmann E15 fault?
This fault occurs when the boiler loses connection with the temperature sensor mounted on the external wall of your home. It is physically caused by either a terminal failure inside the small plastic sensor box or damage to the electrical cable connecting that sensor back to the boiler's main control board. Without this reading, the boiler cannot calculate the correct water temperature and prevents the burner from firing as a safety precaution.
This fault is more common during autumn and winter, as heavy rain or freezing conditions can accelerate corrosion within the sensor casing or cause water ingress in the wiring.
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 E15 fault code
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Source
Viessmann E15 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