BoilerFaultCodesBaxi H.03.05 Fault Code
Also written as H0305 — same fault.
The Baxi H.03.05 fault code means: your boiler is not receiving enough electrical power from your home's mains supply to operate safely.. It appears on 7 Baxi models in our database.
Technical description: Power supply voltage too low
DIY fix possible
Check if there is a partial power cut or 'brownout' in your local areaEnsure the boiler's fused spur switch is fully engaged and not damagedSwitch the boiler off at the main spur, wait 30 seconds, and switch it back on to reset the electronics
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Avoid the next call-out bill
A cover plan would handle faults like H.03.05: no call-out fees, no surprise bills.
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Baxi models that show the H.03.05 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Baxi H.03.05 fault code information on this page is sourced and cross-checked against the official Baxi service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026