BoilerFaultCodesVaillant F.020 Fault Code
Also written as F020 — same fault.
The Vaillant F.020 fault code means: your boiler has detected that the water pressure inside the system has dropped too low, so it has safely shut itself down to prevent any damage.. It appears on 3 Vaillant models in our database.
Technical description: Insufficient/no water in the product. The safety cut-out (SCO) interrupts the gas valve control.
DIY fix possible
Locate the filling loop (a silver flexible hose or internal key) underneath your boiler.Slowly open the valve to allow water to enter the system until the pressure gauge reads between 1.0 and 1.5 bar.Close the valve tightly and check that the error code clears from the display.
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Vaillant models that show the F.020 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant F.020 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 7 July 2026