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Riello NXHM fault L9

Speed difference >15Hz protection between the real and the setting speed (P6 group)

Heat pump

What it means

Speed difference protection exceeding 15Hz between real and setting speed, within the P6 group of inverter protections.

Likely causes

  1. Heat pump system pressure issue
  2. Compressor phase resistance fault
  3. Incorrect U-V-W power line connection sequence between inverter board and compressor
  4. Incorrect L1-L2-L3 power line connection between inverter board and filter board
  5. Faulty inverter board
  6. Air remaining in water system during first operation causing malfunction

Where to start

  1. Check the heat pump system pressure
  2. Check the phase resistance of compressor
  3. Check the U-V-W power line connection sequence between the inverter board and the compressor

The full answer, free

  • 11 more checks in order
  • The readings and component tests from the manual
  • How to put it right, step by step
  • The manual page for this fault (page 67), 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.

Other Riello NXHM fault codes