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Daikin Altherma fault U7-00

Outdoor unit: transmission malfunction between main microcomputer - inverter microcomputer

Heat pump

What it means

Communication abnormality between main and inverter microcomputer.

Likely causes

  1. Faulty main PCB
  2. Faulty inverter PCB
  3. Faulty room thermistor
  4. Bad contact between refrigerant loop and inverter heat sink
  5. Lack of refrigerant
  6. Deviation of thermistor (higher temperature measured than actual)
  7. Communication error between bizone PCB and current loop PCB
  8. Main PCB software fault
  9. Main PCB failure
  10. LD1 not flashing: no operation of LAN adapter
  11. LD2 flashing: TCP/IP communication problem with router
  12. LD3 flashing: communication problem between LAN adapter and indoor unit

Where to start

  1. Perform a check of the main PCB
  2. Perform a check of the inverter PCB
  3. Measure the room temperature and compare to the room temperature shown on the user interface (remote controller)

The full answer, free

  • 20 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