Verified boiler fault code
Baxi H.03.05 Fault Code (Baxi 200/400/600/800 and Assure 500 Combi/System common-code group)
Power supply voltage too low.
Safety disclaimer
Fault code summary
- Manufacturer
- Baxi
- Fault code
- H.03.05
- Fault type
- Electrical
- Severity
- Not specified
- Reset
- Not specified
- Applicable models
- Baxi 200 Combi, Baxi 400 Combi, Baxi 600 Combi, Baxi 800 Combi, Baxi Assure 500 Combi, Baxi 600 System, Baxi 800 System, Baxi Assure 500 System
Quick answer
Power supply voltage too low.
What does this fault code mean?
Power supply voltage too low.
Common causes
- Power supply voltage too low.
Symptoms
This information was not provided in the verified manufacturer source.
What can the homeowner safely check?
- Check only that the boiler has electrical power; use a qualified electrician for electrical diagnosis.
Boiler reset information
Reset information was not provided in the verified manufacturer source. Do not repeatedly reset an unresolved fault.
When should I call an engineer?
Contact a suitably qualified heating engineer when the fault persists, the boiler locks out, or the manufacturer instructions do not resolve it. For gas appliance work in the UK, use a Gas Safe registered engineer.
Engineer diagnosis
- Assess the electrical supply and boiler electrical circuit.
Applicable boiler models
Related fault codes
- A.02.06 — Baxi 200/400/600/800 and Assure 500 Combi/System common-code group
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Return temperature sensor disconnected.
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Flame loss detected five times in 24 hours.
Read fault code - E.01.17 — Baxi 200/400/600/800 and Assure 500 Combi/System common-code group
No water circulation (permanent).
Read fault code - E.04.01 — Baxi 200/400/600/800 and Assure 500 Combi/System common-code group
Flow temperature sensor short-circuited.
Read fault code - E.04.03 — Baxi 200/400/600/800 and Assure 500 Combi/System common-code group
Maximum flow temperature exceeded or flow temperature sensor short-circuited.
Read fault code - E.04.10 — Baxi 200/400/600/800 and Assure 500 Combi/System common-code group
Burner failed to ignite after four attempts.
Read fault code - E.04.12 — Baxi 200/400/600/800 and Assure 500 Combi/System common-code group
Ignition failure — flame monitoring.
Read fault code
Manufacturer documentation
Baxi Error CodesH.03.05 | Power supply voltage too low.
Last verified
2026-09-12
Frequently asked questions
What does Baxi H.03.05 mean?
Power supply voltage too low.