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Daikin Altherma fault AA-02

External backup heater overheated

Heat pump

What it means

Thermal protector is activated. Measured water temperature too high.

Likely causes

  1. Water flow is too low
  2. Air in the water circuit
  3. Wrong setting of [F-0D] pump operation
  4. Water pump software control behaviour based on setting [F-0D]
  5. Dirty water blocking the water filter
  6. NOT enough air purged from the system
  7. Air was purged from the water circuit after filling

Where to start

  1. Check the water flow
  2. Compare the pressure drop of the total system with the water pump characteristics (See check of water pump). Decreased water flow will cause a drop in capacity.
  3. Check the flow sensor.

The full answer, free

  • 5 more checks in order
  • How to put it right, step by step
  • The manual page for this fault (page 28), 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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