P.05 Low

Vaillant P.05 Fault Code

Also written as P05 — same fault.

The Vaillant P.05 fault code means: your boiler is currently undergoing an automatic process to refill or bleed internal air, which happens when the system pressure has been adjusted or replenished.. It appears on 2 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: Fillingtheproduct: Thedivertervalvemovestothemid-position.Theburnerandpumpswitchoff(tofillordraintheproduct). Ifthepressureislowerthan0.03MPa(0.3bar)andthenisabove0.05MPa(0.5bar)forlongerthan15 seconds,theautomaticpurgingfunctionisactivated. Thefunctionisactivefor15minutes.

DIY fix possible

Wait 15 minutes for the automatic purging function to complete its cycle.Ensure your system pressure gauge is between 1.0 and 1.5 bar when the boiler is cool.If the code persists, restart the boiler once the 15-minute countdown has finished.

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Vaillant models that show the P.05 fault code

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

Source

Vaillant P.05 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 7 July 2026