What it means
LB is in the error tables of Mitsubishi's later hydrobox manuals (D and E models) but not in the FTC5 hydrobox list.
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.
- Look for leaks and trapped air
Mitsubishi's first action is to check the water circuit for reduced flow. Look for leaks, and bleed radiators if you hear gurgling.
When to call your installer
Call your installer. Mitsubishi lists reduced flow in the heating circuit, a clogged plate heat exchanger, and outdoor unit faults: refrigerant volume, a valve, the LEV coil or a crushed pipe. Refrigerant work needs an F-gas certified engineer.
A repair visit will usually check the refrigerant charge and the pipe joints for leaks, which needs a qualified refrigeration engineer.
- 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 LB error code mean?
The heat pump has stopped on its high pressure protection. Mitsubishi points first to reduced water flow in the heating circuit, then a clogged plate heat exchanger or an outdoor unit fault. LB is in the error tables of Mitsubishi's later hydrobox manuals (D and E models) but not in the FTC5 hydrobox list.
Can I fix Mitsubishi Ecodan LB myself?
Engineer only (engineer visit). Start with: write the code down and reset once; look for leaks and trapped air. Call your installer. Mitsubishi lists reduced flow in the heating circuit, a clogged plate heat exchanger, and outdoor unit faults: refrigerant volume, a valve, the LEV coil or a crushed pipe. Refrigerant work needs an F-gas certified engineer.
Is Mitsubishi Ecodan LB worth repairing?
Get a quote first. A water flow problem is a routine fix. If the outdoor unit or refrigerant circuit is at fault, get a quote first.
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)
Last reviewed October 2026. Manufacturers update their pages, and your manual is the final word. Spotted a mistake? Email contact@appliance-error-codes.com.