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Daikin Altherma fault U3-00

Under floor heating screed dry out function not completed correctly

Heat pump

What it means

Under floor heating screed dry-out function is interrupted; unit will stop operating.

Likely causes

  1. Faulty or disturbance of the power supply (power supply MUST be within range of nominal operating voltage ±4%)
  2. Power drop
  3. Short circuit
  4. Incorrect or missing software on the PCB
  5. Faulty hydro PCB
  6. Main PCB software fault
  7. Main PCB failure
  8. No power supply
  9. Faulty transformer
  10. PCB malfunction
  11. Damaged or broken wires between power supply terminal and hydro PCB
  12. Incorrectly connected wires
  13. Residual voltage in main circuit capacitors after power off

Where to start

  1. Check if the power supply is compliant with the regulations
  2. First check the power supply to the hydro PCB (3.12.1 Checking procedures)
  3. Locate the HAP LED on the hydro PCB

The full answer, free

  • 17 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 58), 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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