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Mitsubishi Ecodan fault LJ

DHW operation error (type of external plate HEX)

Heat pump

What it means

DHW operation error for systems using an external plate heat exchanger type.

Likely causes

  1. DHW tank water temp. thermistor (THW5) has become detached from its holder
  2. Flow rate of the sanitary circuit may be reduced

Where to start

  1. Check for disconnection of DHW tank water temp. thermistor (THW5)
  2. Check for water circulation pump function

The full answer, free

  • How to put it right, step by step
  • The manual page for this fault (page 50), 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 Mitsubishi manual for the Ecodan. Check the model on the data plate before you order parts.

Other Mitsubishi Ecodan fault codes