E15
Elnur
Return NTC Sensor / Delta-T Fault
Boiler shows E15; may indicate return temperature sensor fault or differential temperature error.
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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 return NTC sensor, Poor contact with return pipe, Blocked return pipe or valve closed, Pump not circulating correctly
How to Fix / Troubleshooting
Safety first: Switch off power and allow the system to cool before touching pipework.
- Check valves and flow: Ensure all isolation valves on the return side of the boiler are fully open. Verify that thermostatic radiator valves are not all closed, which can restrict return flow.
- Inspect return sensor: Locate the return NTC on the return pipe. Confirm it is firmly attached and insulated from ambient air.
- Test sensor: Measure resistance and compare with the flow sensor at the same temperature. Large discrepancies indicate a faulty sensor.
- Check pump performance: Poor circulation can cause abnormal temperature differences. Confirm the pump is running and sized correctly for the system.
- Replace sensor if needed: Fit a new return NTC sensor if faulty and retest the boiler.
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Repair Difficulty
Medium
3/5
Required Part
Return NTC Temperature Sensor
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