What it means
The installation manuals group E6 to EF as "Communication failure between FTC and outdoor unit" and list E9 and EE separately. The service manual describes E6 as a reception error and E7 as a transmission error.
What to check, in order
- Check the outdoor unit is switched on
Mitsubishi's first action is to check the outdoor unit has not been turned off. Check its isolator switch and its circuit breaker.
- Switch both units off and on again
The service manual has the engineer power the indoor and outdoor units off and on again. Switch back on straight away.
- Write the code down if it returns
Make a note of the code and contact your installer.
When to call your installer
Call your installer. Mitsubishi lists loose, shorted or wrongly wired connections on the cable between the units, electrical noise, and faults on the FTC board or the outdoor unit's board.
Quick answers
What does the Mitsubishi Ecodan E6-EF error code mean?
The indoor unit's control board (the FTC) isn't getting proper signals from the outdoor unit, so the heat pump can't run. The installation manuals group E6 to EF as "Communication failure between FTC and outdoor unit" and list E9 and EE separately. The service manual describes E6 as a reception error and E7 as a transmission error.
Can I fix Mitsubishi Ecodan E6-EF myself?
Easy (about 10 minutes). Start with: check the outdoor unit is switched on; switch both units off and on again; write the code down if it returns. Call your installer. Mitsubishi lists loose, shorted or wrongly wired connections on the cable between the units, electrical noise, and faults on the FTC board or the outdoor unit's board.
Is Mitsubishi Ecodan E6-EF worth repairing?
Worth fixing. If the outdoor unit had simply been switched off, it costs nothing. Otherwise Mitsubishi points to the cable between the units or a circuit board.
Checked against
- Ecodan FTC5 Hydrobox Installation Manual, EHS(D)(C)-MEC / EHPX-VM2C (RG79D954H05) (PDF)
- Ecodan Hydrobox EHSC/EHSD series (D models) Installation Manual, error code table (manualslib copy)
- Ecodan Hydrobox EHSD/ERSD series (E models) Installation Manual DG79T728H01, error code table (manualslib copy)
- Ecodan Cylinder Unit Service Manual OCH714A, EHST/ERST/EHPT D models (PDF)
- Ecodan PUZ-WM(50-60-85-112) Outdoor Unit Service Manual (OCH727A) (PDF)
Last reviewed October 2026. Manufacturers update their pages, and your manual is the final word. Spotted a mistake? Email contact@appliance-error-codes.com.