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Mitsubishi Ecodan fault L8

Heating operation error (code 3 - main circulation)

Heat pump

What it means

'3' is displayed in Request code 567 in Running information. Applicable in Heating/FS modes. L8 is displayed if all of the following occur: a) No change on THW1 and THW5 (under 1°C for 20 minutes from unit starts operation); b) No change on THW1 (under 1°C for 10 minutes from booster heater starts operation); c) THW1 - THW2 < -5°C (for 10 minutes continuously).

Likely causes

  1. Failed thermistor TH1A, TH2, THW1, THW2, THWB1, THW5, THWB2, TH1B, THW6, THW7, THW8, or THW9
  2. THW1 has become detached from its holder
  3. Booster heater fault
  4. THW1 or THW2 or THW5 fault
  5. FTC board failure

Where to start

  1. Observe error code screen on main remote controller showing Code, Unit (e.g. FTC), Address, and Tel No. of installer if previously entered
  2. To reset: press F4 button (Reset) on the main remote controller
  3. Then press F3 (Yes) to confirm reset of current error

The full answer, free

  • 19 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 49), 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