BoilerFaultCodesVaillant 0 Fault Code
The Vaillant 0 fault code means: your boiler is currently on standby because your thermostat, timer, or smart heating controls are not telling it to turn on.. It appears on 2 Vaillant models in our database.
Technical description: External controls not calling for heat
DIY fix possible
Check that your room thermostat or smart controller is switched on and set to a higher temperature than the current room temperature.Replace the batteries in your wireless room thermostat or timer.Check that any external programmer or time clock is set to the correct 'on' schedule.
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Vaillant models that show the 0 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant 0 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 31 August 2026