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Grant Aerona R290 fault E21

Compressor phase loss

Heat pump

What it means

Loss of one or more phases to compressor detected.

Likely causes

  1. Cables incorrectly connected
  2. Refrigerant & Drive PCB is faulty
  3. Outdoor air temperature (T4) below 7°C combined with low return (TA) or flow (TB) water temperature below 6°C

Where to start

  1. Check all connections from the Refrigerant PCB (or Refrigerant & Drive PCB for the 16kW model)
  2. Check for red 3 waved lines symbol at top right of touchscreen to confirm demand signal is active
  3. Access 'heat pump schematic' screen (steps 1-3 in section 18.4.1) to view fan, pump and compressor status and water temperatures

The full answer, free

  • 25 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 60), right under the answer
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Safety: Isolate the outdoor unit 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 Grant manual for the Aerona R290. Check the model on the data plate before you order parts.

Other Grant Aerona R290 fault codes