What it means
Mitsubishi's title is "Circulation water temperature overheat protection". The service manual says it shows when water sensor THW1 or THW2 reads 80°C or more for 10 seconds in a row. The installation manuals note it can appear while the heating circuit is being filled.
What to check, in order
- Write the code down and reset once
Switch the system off and clear the code at the main remote controller, then see if it returns.
- Look for leaks
Mitsubishi's action for L3 starts with checking for water leakage, a blocked strainer and the circulation pump. Look for drips around the unit, radiators and pipes.
- Bleed radiators if you hear gurgling
Mitsubishi's operation manual suggests bleeding radiators (if you have them) when air is trapped in the system.
When to call your installer
If it comes back, call your installer. Mitsubishi lists low flow (a weak or faulty pump, trapped air, a blocked strainer or magnetic filter, a leak), faults with the 3-way or 2-way valves or the booster heater relays, a temperature sensor that has come loose or failed, and a control board fault.
Quick answers
What does the Mitsubishi Ecodan L3 error code mean?
The water in the heating circuit has got too hot, so the system has stopped to protect itself. Mitsubishi's first suspect is reduced water flow. Mitsubishi's title is "Circulation water temperature overheat protection". The service manual says it shows when water sensor THW1 or THW2 reads 80°C or more for 10 seconds in a row. The installation manuals note it can appear while the heating circuit is being filled.
Can I fix Mitsubishi Ecodan L3 myself?
Moderate (about 15 minutes). Start with: write the code down and reset once; look for leaks; bleed radiators if you hear gurgling. If it comes back, call your installer. Mitsubishi lists low flow (a weak or faulty pump, trapped air, a blocked strainer or magnetic filter, a leak), faults with the 3-way or 2-way valves or the booster heater relays, a temperature sensor that has come loose or failed, and a control board fault.
Is Mitsubishi Ecodan L3 worth repairing?
Worth fixing. Most of Mitsubishi's causes are water flow, valve, relay or sensor problems that an installer can test and put right.
Checked against
- 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 EHPT(15-17-21-25-30)X-UKH(L)EW1(S-L) Operation Manual, FTC7 (758753) (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.