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Mitsubishi Ecodan fault E9

Applicable error for automatic backup heat source operation

Heat pump

What it means

One of the error codes listed as applicable for automatic switch to backup heat source operation when the outdoor unit stops abnormally.

Likely causes

  1. Heat pump not working
  2. Booster heater cut-out tripped
  3. Booster heater breaker (ECB1) tripped
  4. Booster heater thermal cut-out tripped and cannot be reset using manual reset button
  5. Immersion heater cut-out triggered
  6. Immersion heater breaker (ECB2) tripped
  7. Flow rate of the sanitary circuit may be reduced
  8. Outdoor unit abnormal stop triggers automatic backup operation

Where to start

  1. Check heat pump - consult outdoor unit service manual
  2. Check booster heater thermostat and press reset button if safe (located on side of booster heater under white rubber cap)
  3. Check cause of ECB1 trip and reset if safe

The full answer, free

  • 14 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 17), 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