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Hitachi Yutaki M & Yutaki S fault 15

Water circuit 2 thermistor abnormally (THMwo2)

Heat pump

What it means

Water Circuit 2 thermistor (THMwo2) 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 THMwo2
  2. Check THMwo2 thermistor connector for looseness, disconnection, breakage or short-circuit
  3. Check that water check valve (ATW-WCV-01 accessory) with shut-off valve is connected to the water filling point

The full answer, free

  • 11 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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