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Daikin Altherma fault 89-03

Heat exchanger frozen

Heat pump

What it means

Evaporation temperature is too low during defrost, or outlet water after heat exchanger thermistor <6°C during defrost. Unit will NOT stop operating.

Likely causes

  1. Faulty outlet water after heat exchanger thermistor
  2. Faulty hydro PCB
  3. Deviation of thermistor (higher temperature measured than actual).
  4. Faulty room thermistor
  5. Bad contact between sensor and pipe
  6. Deviation of outlet water after backup heater thermistor (lower temperature measured than actual)
  7. Deviation of thermistor (lower temperature measured than actual)
  8. Incorrect refrigerant charge
  9. Faulty expansion valve control
  10. Faulty suction thermistor
  11. Blockages in refrigerant circuit
  12. Faulty discharge pipe thermistor
  13. Domestic hot water tank thermistor measures a higher temperature than actual (component failure)

Where to start

  1. Perform a check of the outlet water after heat exchanger thermistor
  2. Perform a check of the hydro PCB
  3. Check discharge pipe thermistor.

The full answer, free

  • 15 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 22), 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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