Worldwide
Mitsubishi Electric error codes
Mitsubishi Electric split systems with a wired controller show a two-character check code such as P8 or E6, and the remote's CHECK function gives the same code as beeps and lamp flashes. Wall-mounted MSZ units only blink their operation lamp. Ecodan heat pumps show codes such as L9 on the main remote controller indoors. The meanings come from Mitsubishi Electric's technical, service and installation manuals.
- 24 codes
- Air conditioners & Heat pumps
- Checked against official pages
Air conditioners 12 codes
E6 Indoor and outdoor units not communicating
The indoor unit is not receiving a proper signal from the outdoor unit, so the system has stopped.
E9 Communication fault found by the outdoor unit
The outdoor unit has found a fault in the signal link with the indoor unit, so the system has stopped.
P8 Pipe temperature error
The indoor coil isn't getting cold enough in cooling, or warm enough in heating, compared with the room air, so the unit has stopped.
P6 Freeze or overheat protection
The indoor coil got too cold while cooling or too hot while heating, so the unit has stopped to protect itself.
P5 Drain pump or drain overflow fault
Water is not draining away from the indoor unit, so the float switch has stopped the unit to prevent an overflow.
P1 Room temperature sensor fault
The sensor that measures the air coming into the indoor unit is reading as short-circuited or disconnected.
P2 Liquid pipe temperature sensor fault
The sensor on the indoor unit's liquid refrigerant pipe is reading as short-circuited or disconnected.
P9 Indoor coil temperature sensor fault
The sensor on the indoor coil (the condenser/evaporator pipe) is reading as short-circuited or disconnected.
U2 High discharge temperature or low refrigerant
The refrigerant leaving the outdoor unit's compressor is running too hot.
U4 Outdoor unit sensor fault
One of the temperature sensors in the outdoor unit is reading as short-circuited or disconnected while the compressor runs.
UP Compressor overcurrent
The outdoor unit cut power to the compressor because it was drawing too much current.
U8 Outdoor fan stopped
The outdoor unit's fan isn't turning at the speed it should, so the unit has stopped to protect itself.
Heat pumps 12 codes
L9 Low water flow in the heating circuit
The flow sensor or a flow switch has found too little water moving round the heating (primary) circuit, so the heat pump has stopped to protect itself.
L3 Heating water overheat protection
The water in the heating circuit has got too hot, so the system has stopped to protect itself.
L6 Heating water freeze protection
The water in the heating circuit has got close to freezing, so the system has stepped in to protect itself.
L5 Indoor temperature sensor fault
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.
L8 Heating operation error
The system started heating but the water temperature sensors didn't see the change the controller expected, so it has flagged a heating fault.
LB High pressure protection
The heat pump has stopped on its high pressure protection.
P6 Plate heat exchanger freeze protection
The heat pump has stopped to keep the water in its plate heat exchanger from freezing.
E0-E5 Remote controller communication fault
The main remote controller and the indoor unit's control board (the FTC) have stopped exchanging data properly.
E6-EF Indoor and outdoor units not communicating
The indoor unit's control board (the FTC) isn't getting proper signals from the outdoor unit, so the heat pump can't run.
E9 Outdoor unit gets no signal from indoor unit
The outdoor unit isn't receiving signals from the indoor unit, so the two can't work together.
J1-J8 Wireless remote controller not communicating
The wireless receiver hasn't heard properly from a wireless remote controller for 15 minutes.
U4 Outdoor unit temperature sensor fault
One of the temperature sensors (thermistors) in the outdoor unit is reading as open or short circuit.
No codes of that type for this brand.
Good to know
- Air conditioners: MSZ wall units on their handheld remote don't show letter codes. Mitsubishi's MSZ-FH and MSZ-AP service manuals say the indoor fan stops and the OPERATION INDICATOR lamp blinks instead: fast continuous blinking for a wiring or signal fault between the units, or a count followed by a 2.5-second gap: 2 for a room or coil sensor, 3 for the indoor fan motor, 4 for the indoor control board, 5 for the outdoor power system, 6 for outdoor sensors, 7 for the outdoor control board and 14 or more for other faults.
- Air conditioners: Mitsubishi's operation manual says that if the code and the operation lamp both flash, the unit has stopped: note the unit number and code, switch off the power and contact your dealer or installer. If only the code flashes, the unit keeps running but should still be checked. On a PAR-40MAAU wired controller, F4 or the ON/OFF button resets the error.
- Air conditioners: Not faults: in heating the unit can stop for up to about 10 minutes while the outdoor unit defrosts, and it won't restart for about 3 minutes after being switched off. Mitsubishi says to wait in both cases.
- Ecodan heat pumps: Mitsubishi's operation manuals say to make a note of the error code number and contact your installer, and that users should not attempt to repair the system themselves. Ecodan systems are normally fitted and serviced by an MCS-certified installer.
- Ecodan heat pumps: To clear a code, the installation manuals say to switch the system off first. Then, depending on the controller: hold button E for 3 seconds (FTC5 manual), press F4 (RESET) on controllers with function buttons, or touch RESET on the FTC7 touchscreen controller.
- Ecodan heat pumps: Don't leave the system switched off at the mains in cold weather. The FTC7 operation manual warns that freeze protection will not operate while the unit is off or unpowered, and says not to turn off the power or drain the heating water.
Official help pages
- Mitsubishi Electric SLZ-KF09/12/15/18NA1 ceiling cassette (M-series) Technical & Service Manual TCH118A (PDF)
- Mitsubishi Electric SLZ-M15-60FA ceiling cassette Technical & Service Manual OCH522 (PDF)
- 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)
Every code page links the exact pages it was checked against. Last reviewed October 2026.
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344 codes from 24 brands, each one checked against the maker's own manuals and support pages.