BoilerFaultCodesVaillant P.1 Fault Code
Also written as P1 — same fault.
The Vaillant P.1 fault code means: your boiler is simply running a routine internal test to check it can operate at its maximum power level after starting up.. It appears on 17 Vaillant models in our database.
Technical description: Test program where the appliance is operated in full load after successful ignition
What causes the Vaillant P.1 fault?
This is not actually a fault, but a built-in safety and performance check. It occurs because the boiler needs to confirm it can safely reach its highest firing rate immediately after the burners have lit. Once the system satisfies itself that everything is venting and heating correctly at full power, the code will disappear and normal operation will resume.
DIY fix possible
Wait for the test to complete automaticallyDo not turn the boiler off while the code is displayedMonitor the display to ensure it returns to a normal temperature reading
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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.
- Vaillant ecoMAX manual (PDF)
- Vaillant ecoMAX System 612 manual (PDF)
- Vaillant ecoMAX 824E manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026