BoilerFaultCodesVaillant F.083 Fault Code
Also written as F083 — same fault.
The Vaillant F.083 fault code means: your boiler is failing to heat up because it cannot detect any water movement or temperature change, which usually indicates that your system pressure has dropped too low.. It appears on 3 Vaillant models in our database.
Technical description: System pressure too low. When the burner starts, no temperature increase is registered at the flow or return temperature sensor.
DIY fix possible
Check your boiler's pressure gauge on the front display; it should be between 1.0 and 1.5 bar.If the pressure is below 1.0 bar, locate the filling loop (usually a silver braided hose under the boiler).Open the valves on the filling loop to let water into the system until the gauge reaches 1.5 bar, then ensure the valves are fully closed.
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Vaillant models that show the F.083 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant F.083 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