Baxi · Combi & System 2 platform
H.03.05Power-supply voltage too low
This code applies to Baxi 200 Combi 2, Baxi 400 Combi 2, Baxi 600 Combi 2, Baxi 800 Combi 2, Baxi Assure 500 Combi 2, Baxi 600 System 2, Baxi 800 System 2, Baxi Assure 500 System 2. Fault codes narrow down the likely problem, but they do not replace a model-specific diagnosis.
What you can safely check
- Check for a wider power cut or a tripped consumer-unit circuit without removing the boiler case.
- Use a qualified electrician or Gas Safe engineer for further diagnosis.
How an engineer may fix it
Verify supply voltage, polarity, earthing, fuses, harnesses and appliance electronics; correct the electrical supply or replace the failed component.
Manufacturer source: Baxi Professional — Boiler Error Codes. Checked 15 August 2026. The appliance manual and an engineer’s on-site diagnosis take precedence. Never remove the boiler case yourself.