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Mitsubishi Ecodan fault L4

Tank water temperature overheat protection

Heat pump

What it means

Error code displayed when THW5 detects a temperature ≥ 75ºC for 10 consecutive seconds. Applicable in DHW/Heating/Cooling/LP/FS/OS modes.

Likely causes

  1. 3-way valve actuator fault
  2. Immersion heater relay (IHC) operating fault
  3. THW5 fault
  4. FTC board failure

Where to start

  1. Electrically test 3-way valve actuator to determine fault
  2. Operate 3-way valve manually using the main remote controller (refer to <Manual operation> in 9-4)
  3. Check immersion heater relay (IHC)

The full answer, free

  • 5 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 47), 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