BoilerFaultCodesVaillant P.3 Fault Code
Also written as P3 — same fault.
The Vaillant P.3 fault code means: your boiler is undergoing a temporary calibration process where it checks its heating settings; it is not a fault, but a normal status message.. It appears on 13 Vaillant models in our database.
Technical description: Not available
What causes the Vaillant P.3 fault?
This code appears when the boiler’s electronic control unit is performing a routine check of its burner and gas settings. It happens automatically to ensure the boiler is burning gas as efficiently and safely as possible. You may notice this when the boiler is first switched on or after a period of intense use.
DIY fix possible
Wait approximately 15 minutes for the program to finishEnsure your radiator valves are open to allow heat flow during the testMonitor the display to see if it returns to a standard temperature reading
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Gas Safe Register →Vaillant models that show the P.3 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant P.3 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 27 April 2026