P.03 Low

Vaillant P.03 Fault Code

Also written as P03 — same fault.

The Vaillant P.03 fault code means: your boiler is currently running a specific commissioning program typically used during installation or testing, meaning it is not in its normal operating mode.. It appears on 6 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.
Typical repair cost £0-80 (including labour)

DIY fix possible

Press the 'Back' button (left arrow) on the control panel to see if the display returns to the standard pressure/temperature reading.Turn the boiler off and back on at the main isolation switch (fused spur).Wait for the program to finish its cycle, which usually takes about 15 minutes.

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.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 27 April 2026