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Hitachi Yutaki M & Yutaki S fault 25

Auxiliary sensor 3 thermistor abnormally (THMaux3)

Heat pump

What it means

Auxiliary sensor 3 thermistor (THMaux3) abnormal reading detected.

Likely causes

  1. Loose, disconnected, broken or short-circuited connector
  2. Loose connector
  3. Disconnected connector
  4. Broken connector

Where to start

  1. Check connector and wiring of THMaux3
  2. Check THMaux3 thermistor connector for looseness, disconnection, breakage or short-circuit
  3. Confirm unit is capable of heating and cooling, and cooling operation is enabled, before this function is available

The full answer, free

  • 3 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 336), 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 Hitachi manual for the Yutaki M & Yutaki S. Check the model on the data plate before you order parts.

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