BoilerFaultCodesVaillant P.01 Fault Code
Also written as P01 — same fault.
The Vaillant P.01 fault code means: your boiler is operating normally and performing a standard adjustment to its heating power level.. It appears on 11 Vaillant models in our database.
Technical description: The burner operates with an adjustable heat input in heating or domestic hot water mode
What causes the Vaillant P.01 fault?
This fault occurs when the boiler's internal diagnostic program fails to complete its high-performance test correctly. It is usually triggered manually by an engineer during a service or installation, and the error suggests that the system couldn't maintain the required heat output to finish the check. The most common reason is a sensor reading an unexpected temperature or the test being interrupted before the sequence was finished.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Vaillant models that show the P.01 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant P.01 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.
- Vaillant ecoFIT Pure 425 manual (PDF)
- Vaillant ecoFIT Pure 835 manual (PDF)
- Vaillant Home Combi 35 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026