BoilerFaultCodesVaillant P.1 Fault Code
Also written as P1 — same fault.
The Vaillant P.1 fault code means: your boiler is currently running a self-test at maximum power to ensure everything is working correctly after it has started up.. It appears on 14 Vaillant models in our database.
Technical description: Test programme where the appliance is operated in full load after successful ignition.
What causes the Vaillant P.1 fault?
This isn't actually a fault, but rather a temporary status code triggered when the boiler is performing a safety and performance check. After ignition, the control system forces the boiler to run at its highest power setting to verify that the gas valve and fan are operating correctly. Once the internal sensors are satisfied that the burner is stable at full capacity, the code will disappear and the boiler will return to normal operation.
DIY fix possible
Wait for the test to complete automaticallyMonitor the display to see if it returns to its normal temperature readingIf the code persists for more than 15 minutes, try restarting the boiler
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Gas Safe Register →Vaillant models that show the P.1 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant P.1 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