BoilerFaultCodesVaillant P.0 Fault Code
Also written as P0 — same fault.
The Vaillant P.0 fault code means: your boiler is currently running a self-cleaning routine to remove trapped air bubbles from the system.. It appears on 14 Vaillant models in our database.
Technical description: Bleeding test program. The heating circuit and hot water circuit (when accessories are fitted) is bled via the automatic air vent (the cap on the automatic air vent must be loosened).
What causes the Vaillant P.0 fault?
This code appears when the boiler detects or suspects that air is trapped inside the internal pipework or heat exchanger. It is often triggered automatically after the system has been drained for a repair or when the water pressure has recently been topped up. The boiler runs this program to safely push those air bubbles out through an internal valve to prevent noisy operation or overheating.
This is more common in autumn when homeowners top up their system pressure or bleed their radiators for the first time before turning the heating on for winter.
DIY fix possible
Wait for the program to finish, which usually takes about 6.5 minutes.Ensure the small screw cap on the internal automatic air vent is slightly loosened.Check your boiler pressure gauge and top it up if it has dropped during the process.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Vaillant models that show the P.0 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant P.0 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