Baxi fault code E.04.01 means the flow-temperature sensor is short-circuited. Baxi lists this exact meaning for applicable Combi 2 and System 2 boilers.
The sensor helps the boiler monitor the temperature of water leaving the appliance. E.04.01 means the controls have detected an electrical condition in that sensing circuit which is outside the expected range. The code does not prove the sensor itself is the only failed part.
What does Baxi E.04.01 mean?
The boiler needs reliable flow-temperature information to regulate heating and protect the appliance. A short-circuit reading prevents the controls from trusting that information, so the boiler may stop or restrict operation.
“Short-circuited” is a technical fault description, not a homeowner repair instruction. Do not open the casing, test wires or attempt to replace the sensor.
Which Baxi boilers use E.04.01?
Baxi places E.04.01 in its current Combi & System 2 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 ranges may use different code systems. Check the model name visible on the appliance and use only its matching user guide. Similar numbers on an older boiler can mean something different.
What is a flow-temperature sensor?
The flow-temperature sensor reports the temperature of water leaving the boiler for the heating system. Its information helps the boiler decide how to control heat safely and efficiently.
It is an internal sensing component. Resistance readings, electrical tests, connectors and wiring are service tasks, even if an online video makes them look simple.
Does E.04.01 mean the sensor has failed?
Not necessarily. The fault could involve the sensor, an approved connection, wiring, the control board or another condition affecting the signal. The code points to the circuit that needs checking but does not make the final decision about parts.
An engineer should test the appliance using the model-specific Baxi procedure before anything is replaced. This avoids unnecessary parts and ensures the temperature-control system is checked as a whole.
How is E.04.01 different from E.04.02?
Baxi defines E.04.01 as a short-circuited flow-temperature sensor. E.04.02 is a separate code meaning the flow-temperature sensor is disconnected. One describes a short-circuit condition; the other describes an absent signal.
E.04.03 is different again: Baxi describes it as maximum flow temperature exceeded or the flow-temperature sensor short-circuited. Record every digit and punctuation mark shown on the display so the engineer receives the correct code.
What can you safely check?
Stay outside the appliance and collect useful information:
- Write down E.04.01 exactly as displayed.
- Confirm the full Baxi model name from the exterior or paperwork.
- Note whether heating, hot water or both have stopped.
- Record the visible system-pressure reading.
- Check whether the property has normal electrical power or recently had an outage.
- Look for visible water around the boiler without touching wet electrical equipment.
- Note whether the fault appeared immediately or after the boiler had been running.
Do not remove covers, test resistance or voltage, touch wiring, reseat connectors, enter installer menus or try a replacement sensor. Do not repeatedly power-cycle the boiler.
Can you reset Baxi E.04.01?
Check 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 or sign of damage.
If E.04.01 remains or returns, stop resetting and arrange repair. A sensor-circuit short cannot be made safe by repeatedly clearing the display.
Is E.04.01 an overheating code?
E.04.01 specifically describes the flow-temperature sensor as short-circuited. It does not by itself say the heating water is physically too hot. Baxi uses other codes for maximum-temperature conditions, including E.04.03 and E.04.08.
Because an unreliable sensor signal can prevent correct temperature control, the boiler should still be professionally checked. Do not alter the flow-temperature setting in an attempt to cancel the fault.
What will an engineer do?
A Gas Safe registered engineer will confirm the model, review the fault history and follow Baxi’s service information for the flow-temperature sensing circuit. They can determine why the short-circuit signal is present, complete the appropriate repair and verify normal operation.
If you smell gas, suspect carbon monoxide or hear a carbon-monoxide alarm, follow current Gas Safe Register emergency advice rather than waiting for an ordinary repair appointment.
What information helps when booking?
Provide the E.04.01 code, full model name, visible pressure, whether heating or hot water works, and when the fault first appeared. Our boiler help guides explain other messages, while all sensor and electrical work should remain with the engineer.
Is your Baxi showing E.04.01?
Book Incredaboil’s fixed-price boiler repair for a clear price and an engineer visit aimed at fixing the sensor-circuit fault and restoring normal operation.
Quick answers about Baxi E.04.01
What does E.04.01 mean on a Baxi boiler?
It means the boiler has detected a short-circuit condition involving its flow-temperature sensor.
Does the sensor definitely need replacing?
No. The code identifies the affected circuit, but testing is needed to determine the actual repair.
Is E.04.01 the same as E.04.02?
No. E.04.01 describes a short circuit; E.04.02 means the flow-temperature sensor is disconnected.
Can I test the sensor myself?
No. Keep the casing closed and leave sensor, wiring and control-board testing to a qualified engineer.