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Hitachi Yutaki M & Yutaki S fault 21X

Module X is in alarm state (sub unit)

Heat pump

What it means

Module X (X stands for the module number) is determined to be in alarm state when that module is in alarm or the YUTAKI CASCADE CONTROLLER lost communication with that specific module.

Likely causes

  1. Slave unit alarm
  2. Lost communication with specific module
  3. Sub unit alarm

Where to start

  1. Identify module number X and check its alarm status
  2. Check communication between YCC and module X
  3. Check module X for active alarm

The full answer, free

  • 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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