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Vaillant aroTHERM fault LHM37

Comfort protection mode active

Heat pump

What it means

The product is in Comfort protection mode. The product has detected a permanent fault and continues to run with restricted comfort. The maintenance symbol is shown in the display indicating restricted operation, not full fault lockout.

Likely causes

  1. Permanent fault detected by the product's control system
  2. Permanent internal fault detected by the product
  3. Building power supply switched off
  4. Domestic hot water or heating set to off, or temperature set too low
  5. Air in the heating installation
  6. Extended pump inactivity leading to seizing/sticking
  7. Prolonged pump inactivity leading to seizing/sticking
  8. Pump inactivity leading to sticking/seizure
  9. Extended pump inactivity (23 hours) risking seizure
  10. Pump inactivity for extended period Pump stiction after extended idle period Pump inactivity for extended period
  11. Negative outdoor temperatures Heat pump fault Power cut Defective compressor
  12. System control failure
  13. Power cut
  14. Defective compressor

Where to start

  1. Check display for maintenance symbol
  2. Consult a competent person for diagnosis of the underlying permanent fault
  3. Consult a competent person for further diagnosis

The full answer, free

  • 36 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 10), 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