Baxi fault code E.04.03 means either the maximum flow temperature has been exceeded or the flow-temperature sensor is short-circuited. Baxi lists both possibilities for applicable Combi 2 and System 2 boilers.
This is important because the display does not tell a homeowner which of the two conditions applies. The boiler may have detected water leaving the appliance at an excessive temperature, or it may be receiving an unreliable electrical signal from the temperature-sensing circuit. Keep the casing closed and arrange repair if the code does not clear in accordance with the exact user guide.
What does Baxi E.04.03 mean?
The flow temperature is the temperature of water leaving the boiler for the heating system. The boiler monitors it so heat can be controlled safely. E.04.03 appears when the controls register one of two manufacturer-defined conditions: maximum flow temperature exceeded, or a short circuit involving the flow-temperature sensor.
The code is therefore not proof of overheating and not proof of a failed sensor. An engineer must assess the appliance and its stored fault information before deciding what requires repair.
Which Baxi boilers use E.04.03?
Baxi places E.04.03 in its current Combi & System 2 error-code group. The listed ranges are the Baxi 200, 400, 600 and 800 Combi 2, the Baxi Assure 500 Combi 2, and the Baxi 600, 800 and Assure 500 System 2.
Other Baxi boilers can use different codes. Confirm the full model name from the outside of the appliance and use only its matching user guide. Never apply reset or operating instructions from a different model.
Does E.04.03 mean the boiler is overheating?
It may mean the maximum flow temperature has been exceeded, but the same code can also indicate a short-circuited flow-temperature sensor. Without proper testing, you cannot tell which description explains the message on your boiler.
Do not assume the radiators or boiler casing will feel unusually hot. Equally, do not ignore the code because the appliance feels normal: a faulty temperature signal can prevent the controls from monitoring heat correctly.
Does E.04.03 mean the sensor needs replacing?
Not necessarily. The sensor circuit is one of the manufacturer-listed possibilities, but a code alone cannot determine the failed part. An engineer may need to consider temperature conditions, circulation, the sensor signal, approved connections and the control system using Baxi’s service procedure.
Do not order a sensor or attempt electrical tests from the display alone. Correct checks are needed to avoid replacing the wrong part and to confirm safe operation after repair.
How is E.04.03 different from E.04.01 and E.04.02?
Baxi defines E.04.01 as the flow-temperature sensor being short-circuited. E.04.02 means the sensor is disconnected. E.04.03 is broader because it can mean either maximum flow temperature exceeded or a short-circuit sensor condition.
Record the complete code exactly. One digit changes the manufacturer’s description and the information an engineer uses to begin checking the boiler.
What can you safely check?
Keep every check external:
- Write down E.04.03 exactly as displayed.
- Confirm the model name from the boiler exterior or paperwork.
- Note whether heating, hot water or both have stopped.
- Record the visible system-pressure reading.
- Check whether radiators became unusually hot before the fault, without touching surfaces that may burn.
- Listen for unusual boiling, banging or rushing sounds from a safe distance.
- Look for visible water around the appliance without touching wet electrical equipment.
- Note whether there was a recent power cut or other work at the property.
Do not remove covers, bleed or alter internal components, change pump or bypass settings, test the sensor, touch wiring or enter installer menus.
Can you reset Baxi E.04.03?
Follow the user guide for your exact model. If it permits a homeowner reset, one careful attempt may be reasonable when there is no smell of gas, carbon-monoxide warning, visible leak near electrics, unusual noise or sign of excessive heat.
If the code remains or returns, stop resetting. A recurring maximum-temperature or sensor-circuit message needs professional repair rather than repeated attempts to keep the boiler operating.
When should you switch the boiler off?
If there is visible leaking, steam, a strong unusual noise, scorching, smoke, or surfaces appear dangerously hot, switch the appliance off only if you can do so safely and seek urgent professional advice. Keep children and pets away.
If you smell gas, suspect carbon monoxide or hear a carbon-monoxide alarm, follow current Gas Safe Register emergency guidance immediately. Those warning signs take priority over the displayed code.
What will an engineer do?
A Gas Safe registered engineer will confirm the model, review the fault history and follow Baxi’s service procedure. They can determine whether the boiler experienced a genuine maximum-temperature condition or whether the flow-temperature sensing circuit produced an incorrect signal.
When booking, provide the full code, model, visible pressure, what was running at the time and any unusual heat or noise. Our boiler help guides cover other messages, while internal circulation, sensor and electrical checks remain with the engineer.
Is your Baxi showing E.04.03?
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Quick answers about Baxi E.04.03
What does E.04.03 mean on a Baxi boiler?
It means maximum flow temperature exceeded or the flow-temperature sensor is short-circuited.
Does E.04.03 prove the boiler overheated?
No. Over-temperature is one possibility; the other is a short-circuit signal from the flow-temperature sensor circuit.
Can I test the sensor myself?
No. Keep the casing closed and leave sensor, wiring and control checks to a qualified engineer.
Can I keep resetting E.04.03?
No. Follow the exact user guide and, if it permits a reset, try it once. A code that remains or returns needs professional repair.