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Daikin Altherma fault L4-00

Outdoor unit: malfunction of inverter radiating fin temperature rise

Heat pump

What it means

Radiating fin thermistor measures a too high temperature, causing the unit to stop operating.

Likely causes

  1. Faulty outdoor unit fan motor
  2. Faulty or disturbance of power supply (power supply MUST be within range of nominal operating voltage ±4%)
  3. Power drop
  4. Short circuit
  5. Faulty inverter PCB
  6. Faulty main PCB
  7. Thermal interface grease NOT applied properly on the heat sink
  8. Deviation of thermistor (higher temperature measured than actual).
  9. Faulty room thermistor
  10. Deviation of thermistor (lower temperature measured than actual)
  11. Bad contact between sensor and pipe
  12. Deviation of outlet water after backup heater thermistor (lower temperature measured than actual)
  13. Bad contact between refrigerant loop and inverter heat sink
  14. Lack of refrigerant

Where to start

  1. Perform a check of the outdoor unit fan motor
  2. Check if the power supply is compliant with the regulations
  3. Perform a check of the inverter PCB

The full answer, free

  • 18 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 55), 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 Daikin manual for the Altherma. Check the model on the data plate before you order parts.

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