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Vaillant aroTHERM fault F.729

Compressor outlet temperature too low

Heat pump

What it means

The compressor outlet temperature is lower than 0 °C for more than 10 minutes or the compressor outlet temperature is lower than -10 °C even though the heat pump is in the operating characteristics.

Likely causes

  1. Compressor outlet temperature lower than 0 °C for more than 10 minutes
  2. Compressor outlet temperature lower than -10 °C even though heat pump is in operating characteristics
  3. Low ambient/outdoor temperature causing heating flow temperature to drop
  4. Heating flow temperature of outdoor unit below 4°C
  5. Low outdoor ambient temperature
  6. Low heating flow temperature at outdoor unit
  7. System control failure
  8. Power cut
  9. Defective compressor
  10. Negative outdoor temperatures Heat pump fault Power cut Defective compressor
  11. Heating flow temperature below 4 °C

Where to start

  1. Checking the high-pressure sensor
  2. Checking that the EEV is working correctly
  3. Check the condenser outlet temperature sensor (subcooling)

The full answer, free

  • 35 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 34), 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