E18
Defro DHW Cylinder Temperature Sensor Error

E18 displayed; controller indicates DHW (domestic hot water) sensor fault

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Possible Causes

Failed DHW NTC sensor, Sensor not in correct position on cylinder, Loose wiring, Corroded sensor pocket

How to Fix / Troubleshooting

Safety: Turn off power and ensure DHW cylinder surface is cool enough to touch.

  • Find the DHW sensor on the hot water cylinder (in a pocket or strapped to the side).
  • Ensure good thermal contact with the cylinder and proper insulation over the sensor.
  • Check wiring continuity back to the Defro controller.
  • Measure sensor resistance and compare to specification; replace if faulty.
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Repair Difficulty

Easy 2/5

Required Part

DHW Temperature Sensor
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