Mitsubishi Electric error codes and flashing lights explained
Most Mitsubishi Electric wall units don't show a code on a screen. Instead, the operation indicator lamp flashes a set number of times. Here is how to count the flashes, what each pattern means according to Mitsubishi Electric's service manuals, the codes ducted and cassette systems show, and when to call an engineer.
- pause between groups of flashes
- 2.5 seconds
- to be sure of the number
- Count twice
- diagnostic visit, deducted
- £125
- we repair systems others installed
- Any fitter
How to read the flashing lamp on a wall unit
Spot the fault
The indoor fan stops and the operation indicator lamp on the front of the indoor unit starts flashing.
Count the flashes
Flashes come half a second apart, then the lamp goes off for about 2.5 seconds before the group repeats. Count two full groups to be sure.
Check for even flashing
If the lamp flashes on and off evenly with no long pause, that's a different fault: the first row in the table below.
Write it down
Note the number of flashes and the model number from the label on the side of the indoor unit.
What the flashes mean on MSZ-LN and MSZ-AP wall units
Mitsubishi Electric's troubleshooting table, in plain English. On the MSZ-LN it's the POWER lamp; on the MSZ-AP, the upper lamp.
| Lamp pattern | What Mitsubishi Electric says it means | What you can do |
|---|---|---|
| Flashing evenly, no pause | No signal from the outdoor unit for 6 minutes: a wiring or communication fault | Do one power reset at the isolator. If it comes back, the wiring or a circuit board needs checking. |
| 2 flashes | Indoor coil sensor or room temperature sensor open or short circuit | Book an engineer to test the sensors. |
| 3 flashes | Indoor fan motor fault: no speed signal while the fan runs | Book an engineer. Don't try to turn the fan by hand. |
| 4 flashes | Indoor circuit board can't read its memory | Book an engineer. The usual fix is a new indoor circuit board. |
| 5 flashes | Compressor stopped on overcurrent or failed to start 3 times within a minute of starting | Book an engineer. The checks include the refrigerant valves, the compressor and the inverter. |
| 6 flashes | Outdoor unit temperature sensor open or short circuit | Book an engineer. |
| 7 flashes | Outdoor circuit board can't read its memory | Book an engineer. |
| 14 flashes or more | Another outdoor fault, which the engineer reads at the outdoor unit | Book an engineer. The checks include the refrigerant valves and the 4-way valve. |
| Lamp lit steadily, outdoor unit not running | Outdoor circuit board can't read its memory | Book an engineer. |
Source: Mitsubishi Electric service manuals OBH766 (MSZ-LN-VG) and OBH788 (MSZ-AP-VG), troubleshooting check table, checked October 2026.
Multi-split: one room won't start
On a multi-split, a room that won't start isn't always a fault. Mitsubishi Electric's manuals say that if one room is set to cooling or dry and another to heating, the room switched on first takes priority. Set every room to the same mode and the waiting unit should start.
Check codes on ducted and cassette systems
Ducted and ceiling cassette units on an SUZ outdoor unit show a check code on the wired controller. With a wireless remote, the self-check reports it as a number of beeps and flashes.
| Wired code | Wireless flashes | Meaning | What you can do |
|---|---|---|---|
| P1 | 1 | Room air (intake) sensor error | Book an engineer. |
| P2, P9 | 2 | Pipe temperature sensor error | Book an engineer. |
| E6, E7 | 3 | Indoor and outdoor units can't communicate | One power reset. Book an engineer if it returns. |
| P4 | 4 | Drain sensor error, or the float switch connector is open | Book an engineer. |
| P5 | 5 | Drain pump error | Switch off if water is leaking and book an engineer. |
| PA | 5 | Compressor forced to stop because of a water leakage problem | Switch off, keep the area dry and book an engineer. |
| P6 | 6 | Freezing or overheating protection | Clean the filters and clear the airflow. Book us if it returns. |
| EE | 7 | Indoor and outdoor units don't match | Book an engineer. |
| E4, E5 | 9 | Remote controller signal receiving error | Book an engineer. |
| Fb | 12 | Indoor unit control board error | Book an engineer. |
| PL | 14 | Abnormality in the refrigerant circuit | Book an F-Gas certified engineer. |
| UP | 2, outdoor | Compressor overcurrent cut-out | Book an engineer. |
| U3, U4 | 3, outdoor | Outdoor unit temperature sensor open or short | Book an engineer. |
| E9 | 1, outdoor | Outdoor unit can't send its signal to the indoor unit | One power reset. Book an engineer if it returns. |
Source: Mitsubishi Electric SUZ-M technical and service manual OCH684G. For outdoor faults, the lamp stays on for about 3 seconds before each group of flashes.
Safe checks before you book
Anyone can do these safely. If the same pattern comes back, stop resetting and book a visit.
- Write down the number of flashes and the model number from the indoor unit's label
- Check the remote's batteries, and that it's set to the mode you want
- Switch off, then clean the air filters behind the front panel
- Clear leaves, bins or covers from around the outdoor unit, keeping hands away from the fan
- Do one power reset: switch off at the isolator or breaker, wait a few minutes, then switch on
What a Mitsubishi Electric repair visit costs
The diagnostic visit covers the first hour on site and comes off the bill if you go ahead. We repair Mitsubishi Electric wall, ducted and cassette systems whoever installed them.
- from£125inc. VAT
Repair diagnostic visit
First hour on site, deducted if you go ahead
Mitsubishi Electric error code questions
Why is the light flashing on my Mitsubishi Electric air conditioner?
It means the unit has found a fault and stopped the indoor fan. The number of flashes in each group tells you which fault. Count two full groups, then check the table above.
What does 5 flashes mean on a Mitsubishi Electric wall unit?
On the MSZ-LN and MSZ-AP, 5 flashes means the compressor has stopped for overcurrent, or failed to start, 3 times within a minute of starting. Mitsubishi Electric's checks include the refrigerant valves, the compressor and the inverter, so it needs an engineer.
What does E6 mean on a Mitsubishi Electric controller?
On ducted and cassette systems with an SUZ outdoor unit, E6 or E7 means the indoor and outdoor units can't communicate. Try one power reset at the isolator. If the code comes back, book an engineer to check the wiring and circuit boards.
Can an engineer see past faults on a Mitsubishi Electric unit?
Yes. Mitsubishi Electric wall units remember the last fault even after the lamp stops flashing. An engineer can recall it with a set-up sequence on the remote, so it's worth mentioning a fault that cleared by itself.