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Vaillant aroTHERM fault F.817

Freq. converter fault: compressor

Heat pump

What it means

Fault detected relating to the compressor or frequency converter, potentially caused by a compressor defect, frequency converter defect, or defective/loose connection cable.

Likely causes

  1. Defect in the compressor (e.g. short circuit)
  2. Defect in the frequency converter
  3. Connection cable to the compressor is defective or loose
  4. Low ambient/outdoor temperature causing heating flow temperature to drop
  5. Heating flow temperature of outdoor unit below 4°C
  6. Low outdoor ambient temperature
  7. Low heating flow temperature at outdoor unit
  8. System control failure
  9. Power cut
  10. Defective compressor
  11. Negative outdoor temperatures Heat pump fault Power cut Defective compressor
  12. Heating flow temperature below 4 °C

Where to start

  1. Measure the winding resistance in the compressor
  2. Measure the frequency converter output between the three phases
  3. Check the wiring harness and plug connections

The full answer, free

  • 33 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 37), 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 Vaillant manual for the aroTHERM. Check the model on the data plate before you order parts.

Other Vaillant aroTHERM fault codes