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Riello NXHM fault P3

Compressor overcurrent protection

Heat pump

What it means

Compressor has drawn excessive current, triggering protection.

Likely causes

  1. Same reason as P1
  2. Power supply voltage of the unit is low
  3. Unit may operate out of its operation range (water temperature too low)
  4. Backup heater power supply incorrect
  5. Backup heater thermal fuse open
  6. Backup heater thermal protector activated
  7. Backup heater contactors broken

Where to start

  1. Check power supply voltage to the unit
  2. Investigate causes listed under P1
  3. Check that the backup heater power supply is correct

The full answer, free

  • 7 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