E05
Sime
Flow Temperature Sensor (NTC) Fault
Boiler shows E05, heating does not start, flow temperature reading is abnormal or fixed
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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 NTC sensor, Shorted NTC sensor, Damaged sensor wiring, Faulty main PCB input
How to Fix / Troubleshooting
Safety first: Isolate electrical power before removing the boiler case or disconnecting any sensors.
- Reset and observe: Reset the boiler once. If E05 reappears immediately, suspect the flow NTC or its wiring.
- Visual inspection: Remove the front cover and locate the flow NTC on the flow pipe or primary heat exchanger. Check for loose or corroded connectors and damaged cables. Reseat the plug firmly.
- Check resistance (engineer task): Disconnect the NTC and measure resistance with a multimeter. Compare to Sime's temperature/resistance chart (e.g., around 10kΩ at 25°C). Replace if readings are far out of range or open/short.
- Inspect PCB connector: Ensure the sensor harness is fully seated on the main PCB and there are no signs of burning or water damage.
- Replace NTC if needed: The sensor is usually inexpensive and straightforward to replace. Ensure the new sensor is correctly clipped and has good thermal contact with the pipe.
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Repair Difficulty
Medium
3/5
Required Part
Flow NTC Temperature Sensor
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