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 operating normally, but it is running at the maximum power setting configured during its last service or installation.. 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: The product runs in heating mode with the maximum heat input set using diagnostics code d.00.

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →
Boiler cover options

Avoid the next call-out bill

A cover plan would handle faults like P.03: no call-out fees, no surprise bills.

Approved partner
Domestic Appliance Guard
Unlimited call-outs, 24/7 helpline, no price-hike promise
Get a quote →

Affiliate links. We may earn a commission at no extra cost to you.

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 7 July 2026