E04
Potterton
Flow Thermistor / NTC Sensor Fault
Boiler shows E04 and will not fire, may occur intermittently during operation
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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
Open-circuit flow NTC sensor, Shorted flow NTC sensor, Damaged sensor wiring harness, Faulty PCB sensor input
How to Fix / Troubleshooting
Safety first: Isolate electrical power before removing any covers.
User checks:
- Reset the boiler once and see if the error clears temporarily.
- Check system pressure is within 1.0–1.5 bar when cold.
Engineer checks:
- Locate the flow NTC sensor on the flow pipe from the heat exchanger.
- Disconnect the sensor and measure resistance at ambient temperature; compare with Potterton resistance/temperature chart.
- Inspect wiring and connector for corrosion or loose pins; repair as needed.
- If resistance is out of range or intermittent when flexed, replace the flow NTC sensor.
- If sensor tests OK, check continuity back to the PCB and test PCB input.
Replacing a faulty flow thermistor is usually straightforward but should be done by a competent person to avoid leaks.
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Repair Difficulty
Medium
3/5
Required Part
Flow NTC Thermistor
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