BoilerFaultCodesVaillant 6 Fault Code
The Vaillant 6 fault code means: your boiler has temporarily stopped heating your home or water because a safety control has triggered, usually due to a temporary build-up of heat.. It appears on 2 Vaillant models in our database.
Technical description: Boiler shut down on CH or DHW thermostat
DIY fix possible
Check that your heating and hot water controls are not set too high.Ensure all your radiator valves are fully open so water can circulate properly.Try resetting the boiler using the reset button once it has had time to cool down.
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Vaillant models that show the 6 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant 6 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