BoilerFaultCodesVaillant F19 Fault Code
The Vaillant F19 fault code means: your boiler has lost connection with a temperature sensor, meaning it cannot safely monitor the heat of the water going to your radiators.. It appears on 2 Vaillant models in our database.
Technical description: Central heating NTC unplugged
What causes the Vaillant F19 fault?
This fault occurs when the boiler's internal computer can no longer detect a signal from the temperature sensors located on the main pipes. The most common reason is that the sensor has developed a hardware failure or the electrical wiring connecting it to the main control board has become loose or damaged. Without this connection, the boiler shuts down as a safety precaution because it cannot tell if the water is becoming dangerously hot.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Vaillant models that show the F19 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant F19 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026