What it means
Mitsubishi's indoor manuals call it "Anti-freeze protection of plate heat exchanger". The PUZ-WM outdoor unit service manual describes P6 more broadly as "Freezing/overheating protection is working".
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.
- Let defrost do its job
Mitsubishi's operation manual says not to speed up defrosting by any means other than those it recommends. Don't try to clear ice from the outdoor unit yourself.
- Look for leaks
Mitsubishi lists reduced water flow, from a clogged filter or a water leak, as the first cause.
When to call your installer
Call your installer. Mitsubishi's service manual lists reduced water flow, low load or very cold inlet water, a faulty water pump, a refrigerant leak, shortage or overcharge, and a faulty expansion valve. Refrigerant checks need an F-gas certified engineer.
A repair visit will usually check the water flow and pressure, the temperature sensors and the refrigerant circuit.
- 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 P6 error code mean?
The heat pump has stopped to keep the water in its plate heat exchanger from freezing. Mitsubishi's service manual says this can trigger in cooling mode or during defrost. Mitsubishi's indoor manuals call it "Anti-freeze protection of plate heat exchanger". The PUZ-WM outdoor unit service manual describes P6 more broadly as "Freezing/overheating protection is working".
Can I fix Mitsubishi Ecodan P6 myself?
Engineer only (engineer visit). Start with: write the code down and reset once; let defrost do its job; look for leaks. Call your installer. Mitsubishi's service manual lists reduced water flow, low load or very cold inlet water, a faulty water pump, a refrigerant leak, shortage or overcharge, and a faulty expansion valve. Refrigerant checks need an F-gas certified engineer.
Is Mitsubishi Ecodan P6 worth repairing?
Get a quote first. Water flow problems are routine. If the refrigerant charge or expansion valve is at fault, get a quote first.
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)
- 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.