BoilerFaultCodesVaillant F.323 Fault Code
Also written as F323 — same fault.
The Vaillant F.323 fault code means: your boiler has trapped air inside its main water circulation system, which is preventing the pump from moving water effectively to provide heat or hot water.. It appears on 3 Vaillant models in our database.
Technical description: Air in the product. The heating pump is dry running.
DIY fix possible
Check the boiler's pressure gauge and ensure it is between 1.0 and 1.5 bar, topping it up using the filling loop if necessaryBleed your radiators throughout the home to release any trapped airRestart the boiler to clear the fault code
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Vaillant models that show the F.323 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant F.323 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