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Daikin Altherma fault 81-01

Mixed water thermistor abnormality

Heat pump

What it means

Outlet water thermistor bizone input is out of range. Unit will not stop operating.

Likely causes

  1. Faulty outlet water thermistor for bizone
  2. Faulty bizone PCB
  3. Deviation of thermistor (higher temperature measured than actual).
  4. Faulty room thermistor
  5. Deviation of thermistor (lower temperature measured than actual)
  6. Bad contact between sensor and pipe
  7. Deviation of outlet water after backup heater thermistor (lower temperature measured than actual)
  8. Domestic hot water tank thermistor measures a higher temperature than actual (component failure)

Where to start

  1. Perform a check of the outlet water thermistor bizone
  2. Perform a check of the bizone PCB
  3. Check discharge pipe thermistor.

The full answer, free

  • 10 more checks in order
  • How to put it right, step by step
  • The manual page for this fault (page 22), 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