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Daikin Altherma fault HC-01

Second tank temperature sensor problem

Heat pump

What it means

Domestic hot water tank thermistor input is out of range (second sensor).

Likely causes

  1. Faulty domestic hot water tank thermistor
  2. Faulty hydro PCB
  3. Deviation of thermistor (higher temperature measured than actual).
  4. Faulty room thermistor
  5. Bad contact between sensor and pipe
  6. Deviation of outlet water after backup heater thermistor (lower temperature measured than actual)
  7. Deviation of thermistor (lower temperature measured than actual)
  8. Incorrect refrigerant charge
  9. Faulty expansion valve control
  10. Faulty suction thermistor
  11. Blockages in refrigerant circuit
  12. Faulty discharge pipe thermistor
  13. Domestic hot water tank thermistor measures a higher temperature than actual (component failure)
  14. Incorrect or missing software on the PCB

Where to start

  1. Perform a check of the domestic hot water tank thermistor
  2. Perform a check of the hydro PCB
  3. Check discharge pipe thermistor.

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 49), 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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