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Daikin Altherma fault U5-00

User interface communication problem

Heat pump

What it means

Communication failure between unit and user interface.

Likely causes

  1. Faulty wiring between the user interface and the unit PCB
  2. User interface (main PCB) receives no power
  3. Faulty hydro PCB
  4. Faulty or disturbance of the power supply (power supply MUST be within range of nominal operating voltage ±4%)
  5. Communication error between bizone PCB and current loop PCB
  6. LD2 flashing: TCP/IP communication problem with router
  7. LD3 flashing: communication problem between LAN adapter and indoor unit

Where to start

  1. Check the communication wiring between the user interface and the unit PCB
  2. Perform a power check of the user interface (main PCB) on the unit
  3. Perform a check of the hydro PCB

The full answer, free

  • 7 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 61), 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.

Other Daikin Altherma fault codes