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Riello NXHM fault E4

Water tank temp. sensor (T5) fault

Heat pump

What it means

Fault with the water tank temperature sensor T5, used for domestic hot water monitoring.

Likely causes

  1. Sensor resistance out of range
  2. T5 sensor connector loosened
  3. T5 sensor connector wet or has water ingress
  4. T5 sensor failure

Where to start

  1. Check the resistance of the sensor
  2. Check if T5 sensor connector is loosened
  3. Check if connector is wet or has water in it

The full answer, free

  • The readings and component tests from the manual
  • How to put it right, step by step
  • The manual page for this fault (page 64), right under the answer
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Safety: Isolate the heat pump and any backup heater, and give the inverter capacitors time to discharge before you open the electrics. Anything on the refrigerant circuit needs F-gas certification.

From the Riello manual for the NXHM. Check the model on the data plate before you order parts.

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