What it means
Mitsubishi's service manual gives three triggers: almost no temperature change (under 1°C) at THW1 and THW5B for 20 minutes after start-up, almost no change at THW1 for 10 minutes after the booster heater switches on, or THW1 minus THW2 below -5°C for 10 minutes.
What to check, in order
- Write the code down and reset once
Switch the system off, clear the code at the main remote controller and see if it returns.
- Call your installer if it returns
Mitsubishi's action is to check and re-attach any temperature sensors that may have come loose, which needs the unit opened.
When to call your installer
Mitsubishi's service manual lists a temperature sensor that has come off its holder or failed, a faulty booster heater, or a control board fault.
A repair visit will usually check the hot water cylinder's immersion heater, the valves and the settings.
- Note the model and serial number. They're on a label on the rating plate on the outdoor unit, and on the indoor unit or cylinder.
- Write down the exact code, and what the appliance was doing when it appeared.
- Check whether it's still under warranty. If it is, the repair may cost you nothing.
Quick answers
What does the Mitsubishi Ecodan L8 error code mean?
The system started heating but the water temperature sensors didn't see the change the controller expected, so it has flagged a heating fault. Mitsubishi's service manual gives three triggers: almost no temperature change (under 1°C) at THW1 and THW5B for 20 minutes after start-up, almost no change at THW1 for 10 minutes after the booster heater switches on, or THW1 minus THW2 below -5°C for 10 minutes.
Can I fix Mitsubishi Ecodan L8 myself?
Engineer only (engineer visit). Start with: write the code down and reset once; call your installer if it returns. Mitsubishi's service manual lists a temperature sensor that has come off its holder or failed, a faulty booster heater, or a control board fault.
Is Mitsubishi Ecodan L8 worth repairing?
Worth fixing. Mitsubishi's first action is re-fitting a dislodged sensor, which is quick for an installer. A booster heater or board fault costs more.
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)
Last reviewed October 2026. Manufacturers update their pages, and your manual is the final word. Spotted a mistake? Email contact@appliance-error-codes.com.