What it means
Mitsubishi's title is "Indoor unit temperature thermistor ... failure", followed by a list of sensors. The FTC5 manual lists THW1, THW2, THW5 and THW6 to THW9. Later manuals name the tank sensor THW5B, or THW5A and THW5B. The service manual treats a reading of -39°C or below as open and 88.5°C or above as short.
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.
- Leave the sensors to your installer
Mitsubishi's action is to check the resistance across the sensor, which means opening the unit. That is an installer job.
When to call your installer
Call your installer. Mitsubishi's service manual lists a loose connector or wire, a faulty sensor, wrong DIP switch settings or a control board fault, and says to compare the sensor's resistance with its table.
A repair visit will usually check the sensor's reading and its wiring.
- 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 L5 error code mean?
One of the water temperature sensors (thermistors) connected to the indoor unit is reading as open or short circuit, so the controller can't trust it. Mitsubishi's title is "Indoor unit temperature thermistor ... failure", followed by a list of sensors. The FTC5 manual lists THW1, THW2, THW5 and THW6 to THW9. Later manuals name the tank sensor THW5B, or THW5A and THW5B. The service manual treats a reading of -39°C or below as open and 88.5°C or above as short.
Can I fix Mitsubishi Ecodan L5 myself?
Engineer only (engineer visit). Start with: write the code down and reset once; leave the sensors to your installer. Call your installer. Mitsubishi's service manual lists a loose connector or wire, a faulty sensor, wrong DIP switch settings or a control board fault, and says to compare the sensor's resistance with its table.
Is Mitsubishi Ecodan L5 worth repairing?
Worth fixing. Mitsubishi lists a loose connection or a faulty sensor first. A control board fault is the costlier possibility.
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.