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Daikin Altherma fault 8H-01

Overheating mixed water circuit

Heat pump

What it means

Water temperature in the mixed circuit is too high.

Likely causes

  1. Faulty outlet water thermistor for bizone
  2. Mixed water temperature exceeds [9-00] setting + 5K
  3. Faulty 3-way valve
  4. Faulty bizone PCB
  5. Deviation of thermistor (higher temperature measured than actual).
  6. Faulty room thermistor
  7. Bad contact between sensor and pipe
  8. Loose or disconnected wires
  9. Damaged connectors or wires
  10. Deviation of outlet water after backup heater thermistor (lower temperature measured than actual)
  11. Deviation of thermistor (lower temperature measured than actual)
  12. Bad contact between refrigerant loop and inverter heat sink
  13. Lack of refrigerant
  14. Open circuit winding
  15. Short circuit winding
  16. LD1 not flashing: no operation of LAN adapter
  17. LD2 flashing: TCP/IP communication problem with router
  18. LD3 flashing: communication problem between LAN adapter and indoor unit

Where to start

  1. Perform a check of the outlet water thermistor bizone
  2. Check the field setting [9-00]
  3. Perform a check of the 3-way valve

The full answer, free

  • 23 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 25), 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