P.03 Low

Vaillant P.03 Fault Code

Also written as P03 — same fault.

The Vaillant P.03 fault code means: your boiler is performing a routine air-bleeding or check program after being switched on or reset, and it is not currently an error that requires a repair.. It appears on 4 Vaillant models in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: Check programme for system without eBUS controller.

DIY fix possible

Wait approximately 5 to 10 minutes for the program to finish automatically.Monitor the display to see if the boiler transitions to a standard temperature reading or '0' status.Ensure all radiator valves are open to help the system clear any trapped air.

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Vaillant models that show the P.03 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Vaillant P.03 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 31 August 2026