Baxi code H.03.05 means the power-supply voltage is too low. Baxi lists it for the applicable Combi 2 and System 2 boiler ranges. It is an electrical-supply message, so it should not be confused with a flame, gas-supply or water-pressure fault.
The boiler needs a stable electrical supply to operate its controls and safety systems. When the voltage falls below the level the appliance expects, it may pause or stop operation and show H.03.05. The code does not tell a homeowner whether the cause is a temporary network issue, a property supply problem or something local to the boiler.
What does Baxi H.03.05 mean?
The official Baxi description is “power supply voltage too low”. In plain English, the boiler has detected that the incoming electrical supply is below its acceptable operating range.
This is different from Baxi H.03.54, which the manufacturer describes as temporary flame loss with shutdown due to low supply voltage. H.03.05 itself identifies the low-voltage condition. Avoid adding a second fault meaning that is not shown on your display.
Which Baxi boilers can show H.03.05?
Baxi places H.03.05 in its Combi & System 2 error-code group. The listed models include the Baxi 200, 400, 600 and 800 Combi 2, the Assure 500 Combi 2, and the Baxi 600, 800 and Assure 500 System 2 boilers.
Other Baxi ranges use different control systems and may show different codes. Check the model name visible on the appliance and consult the matching user guide before using any reset control. A similar-looking code on another boiler make may have a completely different meaning.
Could a power cut cause H.03.05?
A power interruption or wider supply disturbance may coincide with a low-voltage message, but the code alone cannot prove where the issue originated. Safely check whether lights or other appliances in the property are also affected and whether neighbours have reported a power cut. Do not open the consumer unit, boiler casing, fused spur or electrical accessories.
For a power cut in Great Britain, the Energy Networks Association advises calling 105 free to reach the local electricity network operator. If there is damaged network equipment or a fallen power line, keep well away and call 105; call 999 if there is an immediate danger to life.
What can you safely check?
Useful external observations include:
- Write down H.03.05 exactly as displayed.
- Note whether the heating and hot water stopped at the same time.
- Check whether ordinary lights or other appliances are behaving unusually.
- Confirm whether there has just been a power cut or local supply incident.
- Record whether the code clears when the wider electricity supply is confirmed stable.
- Identify the exact Baxi model without removing any boiler panel.
These checks help separate an obvious area outage from a boiler message, but they are not electrical testing. Do not use a multimeter, remove covers, change wiring or replace fuses as a fault-finding experiment.
Should you reset a Baxi H.03.05 code?
Wait until any known power cut has ended and the household supply appears stable. Then consult the user guide for your exact model. If the guide permits a user reset, one attempt using the normal control is reasonable when there is no burning smell, visible damage or sign of overheating.
If H.03.05 remains or returns, stop resetting and arrange a qualified repair. Repeated resets cannot correct an unstable supply or an internal electrical issue, and they can obscure when the problem occurs.
What should you do if there is a burning smell?
If you notice burning, smoke, scorching, sparking or unusual heat around the boiler or its electrical supply, do not touch the appliance. Move away, isolate the electricity only if you can do so without approaching the hazard, and seek urgent help. Call 999 if there is immediate danger or fire.
Never remove the boiler casing or fused-spur cover to investigate. The boiler contains mains-voltage parts as well as gas and combustion components, so internal work must be completed by appropriately qualified professionals.
Can the boiler be used if the code disappears?
If an area power cut has just ended and H.03.05 clears in accordance with the correct user guide, monitor the boiler. If the code returns, appears without a known supply interruption or affects operation repeatedly, book a repair rather than assuming it is harmless.
Intermittent low voltage can be difficult to identify from a single display message. Accurate notes about when it happens—during a wider outage, at a particular time or when other household electrics behave unusually—can help the right professionals investigate efficiently.
What will happen during a repair?
The engineer will confirm the exact model and code history, consider whether the wider electricity supply is involved and use the correct Baxi service information. Depending on what is found, an electrical supply issue may also require an electrician or the electricity network operator. The fault code itself does not prove the boiler needs a particular component.
Keep the boiler closed and provide the model, displayed code and timing when booking. For other manufacturer-specific messages, visit our boiler help guides.
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Quick answers about Baxi H.03.05
What does H.03.05 mean on a Baxi boiler?
Baxi defines H.03.05 as power-supply voltage too low on the applicable Combi 2 and System 2 ranges.
Is H.03.05 a gas-pressure fault?
No. It refers to the electrical supply voltage, not the boiler’s gas pressure or heating-system water pressure.
Can a local power cut trigger H.03.05?
A supply interruption may coincide with the code, but the display cannot prove the source. Check for a known outage safely and call 105 for electricity-network information in Great Britain.
Can I fix H.03.05 myself?
Do not test voltage, open covers or alter wiring. After the supply is stable, use only the reset instruction in the exact model’s user guide. A returning code needs professional attention.