Mitsubishi Electric error codes depend on the range. Mr Slim and Ecodan controllers show two-character codes such as P5, drain overflow protection, and U2, high discharge temperature. City Multi VRF uses four-digit codes such as 1102, a discharge temperature fault, and 1301, a low pressure fault. M-Series wall units blink the OPERATION INDICATOR lamp instead. The same code can mean different things on different ranges.
The tables below come from Mitsubishi Electric's own service and installation manuals, with the range named for each one. Mitsubishi Electric UK also runs an error code lookup for installers.
At a glance
| Code | Range | What Mitsubishi says it means |
|---|---|---|
| P5 | Mr Slim | Drain overflow protection operation |
| P4 | Mr Slim | Drain sensor error / Float switch connector open |
| E6, E7 | Mr Slim | Indoor/outdoor unit communication error |
| U2 | Mr Slim | Abnormal high discharging temperature/49C worked/insufficient refrigerant |
| U1 | Mr Slim | Abnormal high pressure (63H worked) |
| 1102 | City Multi | Discharge temperature fault |
| 1301 | City Multi | Low pressure fault |
| 2502 | City Multi | Drain pump fault |
| L9 | Ecodan | Low primary circuit flow rate detected by flow sensor or flow switch |
| L3 | Ecodan | Circulation water temperature overheat protection |
Source: Mitsubishi Electric service manual OCH697 (Mr Slim), City Multi error code list, and the Ecodan FTC6 installation manual.
How Mitsubishi Electric shows a fault
According to Mitsubishi's service manual for Mr Slim PLA-M ceiling cassettes, when a malfunction occurs both the indoor and outdoor units stop and the operation lamp blinks. On a wired remote controller, the check code appears on the screen, and present and past codes are logged.
With a wireless remote, the code comes from the remote's self-check mode, which the manual for your remote explains. The indoor unit then beeps and blinks its OPERATION INDICATOR lamp, and the number of beeps and blinks gives the code. A pattern that starts with a long ON of about 3 seconds is a fault detected by the outdoor unit. Without that long ON, the fault was detected by the indoor unit. If the unit beeps twice to confirm self-check has started and nothing follows, Mitsubishi says there are no error records.
City Multi controllers show a four-digit code, and some show a two-character version of it as well, so 1102 can also appear as U2. Ecodan main remote controllers show the code with the unit and address. M-Series wall units, such as the MSZ-HR, do not show letter codes at all and blink the OPERATION INDICATOR lamp instead.
One thing to know before using older code lists: TH2, TH3 and TH4 are not error codes. Mitsubishi uses them as the names of thermistors, which is why they appear inside descriptions such as "Pipe (TH2) sensor error".
Mr Slim codes detected by the indoor unit
These come from section 9 of Mitsubishi's OCH697 service manual for Mr Slim PLA-M cassettes. The blink count is what you see on the OPERATION INDICATOR lamp with a wireless remote.
| Blinks | Code | What Mitsubishi says it means |
|---|---|---|
| 1 | P1 | Intake sensor error |
| 2 | P2 | Pipe (TH2) sensor error |
| 2 | P9 | Pipe (TH5) sensor error |
| 3 | E6, E7 | Indoor/outdoor unit communication error |
| 4 | P4 | Drain sensor error / Float switch connector open |
| 5 | P5 | Drain overflow protection operation |
| 5 | PA | Forced compressor error (due to water leakage abnormality) |
| 6 | P6 | Freeze (during cooling operation)/Overheat protection operation (during heating operation) |
| 7 | EE | Combination error between indoor and outdoor unit |
| 8 | P8 | Pipe temperature error |
| 9 | E4, E5 | Communication error between wired remote controller and indoor unit |
| 11 | Pb | Indoor unit fan motor error |
| 12 | Fb | Indoor unit control system error (memory error, etc.) |
| 14 | PL | Refrigerant circuit abnormal |
| Wired only | E0, E3 | Remote controller transmission error |
| Wired only | E1, E2 | Remote controller control board error |
Mr Slim codes detected by the outdoor unit
Mitsubishi notes that the supported codes may vary depending on the connected outdoor unit.
| Blinks | Code | What Mitsubishi says it means |
|---|---|---|
| 1 | E9 | Indoor/outdoor unit communication error |
| 2 | UP | Compressor overcurrent interruption |
| 3 | U3, U4 | Open/short of outdoor unit thermistors |
| 4 | UF | Compressor overcurrent interruption (When compressor locked) |
| 5 | U2 | Abnormal high discharging temperature/49C worked/insufficient refrigerant |
| 6 | U1, Ud | Abnormal high pressure (63H worked)/Overheat protection operation |
| 7 | U5 | Abnormal temperature of heat sink |
| 8 | U8 | Outdoor unit fan protection stop |
| 9 | U6 | Compressor overcurrent interruption/Abnormal of power module |
| 10 | U7 | Abnormality of super heat due to low discharge temperature |
| 11 | U9, UH | Abnormality such as overvoltage or voltage shortage and abnormal synchronous signal to main circuit/Current sensor error |
| 14 | Others | Other errors (refer to the technical manual for the outdoor unit) |
P5: drain overflow protection
P5 is one of the most searched Mitsubishi codes. In the OCH697 manual, P5 is set when the drain float switch detects water for 1 minute and 30 seconds continuously with the drain pump running, and the compressor and indoor fan turn off. The causes Mitsubishi lists are a drain pump malfunction, a defective drain, a clogged drain pump or a clogged drain pipe. That makes P5 a condensate problem rather than a refrigerant one, which our guide to condensate pumps explains.
City Multi four-digit codes
City Multi VRF systems use four-digit check codes. The list below comes from Mitsubishi Electric's City Multi error code list, published by its Singapore business for PUCY and PUMY-CP outdoor units. Where the two sections word a code differently, both are given. UK models can differ, so treat this as a guide and confirm against the manual for your outdoor unit.
| Code | Short code | What Mitsubishi says it means |
|---|---|---|
| 0403 | Ed | Serial communication error |
| 1102 | U2 | Discharge temperature fault (PUCY), compressor temperature trouble (PUMY-CP) |
| 1301 | Low pressure fault (PUCY) | |
| 1302 | UE | High pressure fault |
| 1500 | U7 | Refrigerant overcharge (PUCY), superheat due to low discharge temperature trouble (PUMY-CP) |
| 1501 | U2 | Refrigerant shortage trouble, or closed valve in cooling mode (PUMY-CP) |
| 1503 | P6 | Freeze protection of branch box or indoor unit |
| 2500 | PA | Water leakage |
| 2502 | P5 | Drain pump fault (PUCY), drain overflow protection (PUMY-CP) |
| 2503 | P4 | Drain sensor trouble |
| 4100 | UF | Compressor current interruption (locked compressor) |
| 4210 | UP | Compressor overcurrent interruption/failure in 12 VDC power supply circuit on power circuit board |
| 4220 | U9 | Undervoltage/overvoltage/PAM error/L1 open phase/power synchronization signal error |
| 4230 | U5 | Heat sink temperature trouble |
| 4250 | U6 | Power module trouble or overcurrent trouble |
| 4400 | U8 | Fan trouble (outdoor) |
| 5101 | U3 | Compressor temperature thermistor (TH4) open/short, or air inlet thermistor (TH21) open/short on the indoor unit |
| 5102 | U4 | Suction pipe temperature thermistor (TH6) open/short |
| 5201 | F5 | High pressure sensor (63HS) trouble |
| 5300 | UH | Current sensor trouble |
| 6600 | A0 | Duplex address error |
| 6602 | A2 | Transmission processor hardware error |
| 6603 | A3 | Transmission bus BUSY error |
| 6606 | A6 | Signal communication error with transmission processor |
| 6607 | No ACK error | |
| 6831 | E0/E4 | MA communication receive error (no receive signal) |
| 7100 | EF | Total capacity error |
| 7102 | EF | Connecting unit number error |
| 7130 | EF | Incompatible unit combination |
Code 1102: discharge temperature
1102 means the compressor discharge has run too hot. For PUCY units, Mitsubishi's checks are the refrigerant charge, the operating conditions of the indoor and outdoor units, the indoor and outdoor expansion valves (LEV), that the refrigerant service valve is fully open, the outdoor fan and the TH4 thermistor. For PUMY-CP units, the causes it lists include a stop valve fault, an overheated compressor caused by a shortage of refrigerant, a defective thermistor or board, and a refrigerant system clogged by a foreign object. All of these are engineer checks, and anything involving the refrigerant charge needs an F gas qualified engineer.
Code 1301: low pressure
1301 is a low pressure fault on PUCY outdoor units. Mitsubishi's first check is the low pressure sensor, compared against gauge pressure, which means connecting gauges to the refrigerant circuit. That is a job for an engineer, and a genuinely low pressure often points to a refrigerant shortage, which means a leak to find and repair.
Ecodan heat pump codes
Ecodan air-to-water heat pumps show codes on the main remote controller. These come from Mitsubishi's installation manual for the Ecodan FTC6 flow temperature controller. Some letters overlap with Mr Slim codes but mean different things, so P1, P2 and P6 on an Ecodan are not the same faults as on a Mr Slim.
| Code | What Mitsubishi says it means |
|---|---|
| L3 | Circulation water temperature overheat protection |
| L4 | DHW tank water temperature overheat protection |
| L5 | Indoor unit temperature thermistor failure |
| L6 | Circulation water freeze protection |
| L8 | Heating operation error |
| L9 | Low primary circuit flow rate detected by flow sensor or flow switch |
| LA | Pressure sensor failure |
| LB | High pressure protection |
| LC | Boiler circulation water temperature overheat protection |
| LD | Boiler temperature thermistor (THWB1) failure |
| LE | Boiler operation error |
| LF | Flow sensor failure |
| LH | Boiler circulation water freeze protection |
| LJ | DHW operation error (type of external plate HEX) |
| LL | Setting errors of DIP switches on FTC control board |
| LP | Out of water flow rate range for outdoor heat pump unit |
| P1 | Thermistor (Room temp.) (TH1) failure |
| P2 | Thermistor (Ref. liquid temp.) (TH2) failure |
| P6 | Anti-freeze protection of plate heat exchanger |
| J0 | Communication failure between FTC and wireless receiver |
| J1 to J8 | Communication failure between wireless receiver and wireless remote controller |
| J9 | Communication failure between FTC (Main) and FTC (Sub) |
| E0 to E5 | Communication failure between main remote controller and FTC |
| E6 to EF | Communication failure between FTC and outdoor unit |
| E9 | Outdoor unit receives no signal from indoor unit |
| EE | Combination error between FTC and outdoor unit |
| U, F or A codes | Outdoor unit failure. Refer to the outdoor unit service manual |
For L3, L6 and L9, Mitsubishi says the flow rate may be reduced and to check for water leakage, a blocked strainer and the circulation pump. It adds that the code may show while the primary circuit is being filled, in which case the filling should be completed and the code reset. For J1 to J8, check the wireless remote's battery is not flat and that it is paired with the receiver.
For Ecodan outdoor units, Mitsubishi's OCH439H service manual lists U1 as high pressure, U2 as high discharging temperature, U3 and U4 as thermistor open or short circuits, U5 as heatsink temperature, U6 as the power module and U7 as too low superheat due to low discharge temperature.
M-Series wall units: counting the blinks
Domestic M-Series wall units show faults by blinking the OPERATION INDICATOR lamp rather than with a code. Mitsubishi's service manual for the MSZ-HR tells engineers to check how many times the lamp blinks before starting work. For example, on the MSZ-HR, the left lamp blinking on and off at 0.5-second intervals points to miswiring or a serial signal fault between the indoor and outdoor units.
The meaning of each blink count varies by model, so count the blinks, note the gap between each set, and give the count and the model number to your engineer.
How to reset a Mitsubishi Electric error
- Ecodan. Mitsubishi's FTC6 manual says to press the F4 (RESET) button, then the F3 (Yes) button, to reset the current error.
- Mr Slim and City Multi. Codes are logged by the controller, and Mitsubishi's service manual says to reset the check code logs and restart the unit after finishing service. Switching the power off and on once can clear a one-off fault, but if the code returns, the fault is still there.
- After a power cut. Mitsubishi notes that for about 2 minutes after power-on, the remote controller cannot be operated while the system starts up. That is normal and not a fault.
What you can check safely
- Write it down. Note the code or blink count and the model numbers from the rating labels on the indoor and outdoor units.
- Check the power. Make sure the supply is on and no breaker has tripped.
- Look at the outdoor unit. Make sure nothing is blocking it, such as leaves, a cover or stored items, especially with high pressure or high temperature codes.
- Check the filters. Clogged filters reduce airflow, which Mitsubishi lists among the causes of high pressure faults.
- Look for water. With P4 or P5, check for water at the indoor unit and switch it off if it is dripping.
Safety
Mitsubishi's service manual warns not to alter the unit and to ask a dealer or an authorised technician to install, relocate and repair it. On Ecodan systems, the FTC6 manual cautions that the pump valves may be hot and warns not to touch switches with wet hands because of the risk of electric shock. Any work on the refrigerant circuit needs the F gas qualifications set out by GOV.UK.
When to call an engineer
- Any code that returns after one power reset.
- Pressure and temperature codes, such as U1, U2, 1102, 1301 and 1302.
- Compressor and power codes, such as UF, UP, U6 and U9.
- Communication codes such as E6, E9 or 0403, which often point to the wiring between the units.
- P5 or P4 that comes back after the drain has been checked.
Our air conditioning repair team works on Mitsubishi Electric systems across London, and our guide to VRF air conditioning explains how City Multi systems work.
Questions people ask about Mitsubishi Electric error codes
What does P5 mean on a Mitsubishi air conditioner?
On Mr Slim units, P5 is drain overflow protection operation. The float switch has detected water for 90 seconds with the drain pump running, so the compressor and indoor fan stop. Mitsubishi lists a drain pump fault, a defective drain or a clogged pump or pipe as the causes.
What is error code 1102 on a Mitsubishi?
1102 is a City Multi code for a discharge temperature fault, also worded as compressor temperature trouble, and it can show as U2. Mitsubishi's checks include the refrigerant charge, the expansion valves, the service valve, the outdoor fan and the TH4 thermistor.
What does 1301 mean on a Mitsubishi?
1301 is a low pressure fault on City Multi PUCY outdoor units. Mitsubishi's first check is the low pressure sensor against gauge pressure, which is an engineer's job.
What does E6 mean on a Mitsubishi Electric air conditioner?
On Mr Slim, E6 and E7 are indoor and outdoor unit communication errors, shown as 3 blinks with a wireless remote. On an Ecodan, E6 to EF mean a communication failure between the FTC and the outdoor unit, and Mitsubishi says to check the outdoor unit has not been turned off and the cable is not damaged or loose.
How do I reset a Mitsubishi Ecodan error?
Press the F4 (RESET) button on the FTC6 main remote, then the F3 (Yes) button. If the code comes back, the fault is still there and needs an engineer.
Why is the light flashing on my Mitsubishi air conditioner?
A blinking OPERATION INDICATOR lamp usually means the unit has stopped with a fault. On M-Series wall units, the number of blinks points to the fault. Count them and note the model number before calling an engineer.
Getting a Mitsubishi Electric fixed
Note the code or blink count, the range and the model numbers, check the power and the outdoor unit, and try one reset. If the code comes back, an engineer will know where to start. Planned air conditioning maintenance keeps filters, drains and condensers clean, which stops many of these codes appearing.
Last updated: 4 November 2026
Written by
Ali Elm
Ali is the Head of Operations at Be Cool Refrigeration with over a decade of hands-on experience in HVAC and commercial refrigeration. He oversees every installation, repair, and maintenance project, making sure the work meets the highest standards. Ali holds full F-Gas certification and has worked across residential, commercial, and industrial refrigeration systems throughout London and the South East. When he is not on site, he writes these guides to help business owners and homeowners understand their cooling systems better.