E04
EHC
Primary Flow Temperature Sensor Fault (NTC Open/Short)
Boiler displays E04 and will not fire, often immediately on power-up.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Faulty flow NTC sensor, Damaged sensor wiring harness, Poor connection at PCB, PCB input fault
How to Fix / Troubleshooting
Safety: Isolate power before accessing internal components.
User checks:
- Reset the boiler once. If E04 reappears immediately, a sensor or wiring fault is likely.
Engineer checks:
- Locate the primary flow NTC sensor on the EHC boiler flow pipe leaving the heat exchanger.
- Disconnect the sensor and measure its resistance at ambient temperature; compare with EHC resistance/temperature chart.
- Inspect the sensor plug and wiring for corrosion, damage or loose pins; repair or replace as needed.
- Check continuity from the sensor connector back to the PCB.
- If resistance is correct and wiring is sound, suspect a faulty PCB temperature input.
Replace the flow NTC sensor with an EHC-compatible part if readings are out of specification.
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Repair Difficulty
Medium
3/5
Required Part
Primary Flow NTC Sensor
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