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All Mitsubishi Electric error codes

This page brings together Mitsubishi Electric error codes sorted by fault type: what each code means, its likely causes, and what you can safely check before calling a professional.

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The Mitsubishi Electric codes on this page, grouped by fault type.

temperature sensor

E28 E3 E35 E37 E38 E4 E53 E56 E9 L5 LD P1 P2

general fault

E40 E42 E54 L8 LE LF LL

circuit board

E34 E51 LA LB

compressor

E55 E59 E60 P5

power module

E41 P2 P4 P6

discharge temperature

E36 E39 Ed U3

low pressure

power supply

communication

fan

defrosting

high pressure

reversing valve

E32

Temperature sensor — Mitsubishi Electric

These codes indicate a sensor that’s no longer returning a consistent value. The fault almost always comes from the sensor itself or its connector, rarely from the unit.

Code E28Informationair-to-water

Fault on the remote room temperature thermistor in the remote control

Affected models: Yack Modul’O

Code E3Medium severityair-to-air

Wired remote control transmission error

Possible causes

Remote control cable
Interference

Affected models: MSZ-AP, MSZ-AY, MSZ-EF, MSZ-LN, MSZ-HR

This fault requires a qualified technician. Do not open the unit.

Code E35Informationair-to-water

The temperature on the outdoor heat exchanger is too high, or the heat exchanger thermistor is faulty

Affected models: Yack Modul’O

Code E37Informationair-to-water

Fault on the outdoor unit heat exchanger thermistor

Affected models: Yack Modul’O

Code E38Informationair-to-water

Fault on the outdoor air thermistor

Affected models: Yack Modul’O

Code E4Medium severityair-to-air

Remote control signal reception error (communication between remote control and indoor unit)

Possible causes

Remote control cable
Addressing

Affected models: MSZ-AP, MSZ-AY, MSZ-LN

This fault requires a qualified technician. Do not open the unit.

Code E53Informationair-to-water

Fault on the suction thermistor

Affected models: Yack Modul’O

Code E56Informationair-to-water

Fault on the power transistor thermistor

Affected models: Yack Modul’O

Code E9Medium severityair-to-air

Indoor/outdoor communication error (the outdoor unit isn’t receiving any signal)

Possible causes

Connecting wiring
Unit not powered

Affected models: MUZ-AP, MUZ-AY, MUZ-LN, MUZ-HR

This fault requires a qualified technician. Do not open the unit.

Code L5Medium severityair-to-water

Fault on an indoor module thermistor (THW1, THW2, THW5, THW6, THW7, THW8, THW9)

Possible causes

Thermistor disconnected or faulty

Affected models: Ecodan Hydrobox, Ecodan All-in-One, EHPX, ERSC

This fault requires a qualified technician. Do not open the unit.

Code LDMedium severityair-to-water

Boiler temperature thermistor fault (THWB1, THWB2)

Possible causes

Faulty thermistor
Loose connection

Affected models: Ecodan, Ecodan Hydrobox, PUHZ, EHPX, ERSC

This fault requires a qualified technician. Do not open the unit.

Code P1Medium severityair-to-water

Room temperature thermistor fault (TH1)

Possible causes

Thermistor open or short-circuited

Affected models: PUHZ, PUHY, PQHY, Zubadan

This issue requires a qualified technician. Do not open the unit.

Code P2Medium severityair-to-water

Refrigerant liquid temperature thermistor fault (TH2)

Possible causes

Thermistor open or short-circuited

Affected models: PUHZ, PUHY, Zubadan

This issue requires a qualified technician. Do not open the unit.

General fault — Mitsubishi Electric

These codes don’t point to a specific part: the unit is signaling that an internal safety feature has tripped.

Code E40Informationair-to-water

High pressure fault (pressure switch 63H1 triggered)

Affected models: Yack Modul’O

This issue requires a qualified technician. Do not open the unit.

Code E42Informationair-to-water

Overcurrent

Affected models: Yack Modul’O

Code E54Informationair-to-water

Low pressure fault

Affected models: Yack Modul’O

This issue requires a qualified technician. Do not open the unit.

Code L8Medium severityair-to-water

Heating operation error (temperature not reached)

Possible causes

Insufficient water flow
Flow sensor incorrectly positioned
Insufficient output for the demand
Low refrigerant level

What you can check

Bleed air from the circuit
Clean the particle filter
Check that the heating circuits are open

Affected models: Ecodan, Ecodan Hydrobox, PUHZ, EHPX, ERSC

This issue requires a qualified technician. Do not open the unit.

Code LECritical severityair-to-water

Backup boiler operation error

Possible causes

Thermistor disconnected
Incorrect wiring
Boiler faulty or out of fuel
Faulty FTC board

Affected models: Ecodan Hydrobox, Ecodan All-in-One, EHPX, ERSC

This issue requires a qualified technician. Do not open the unit.

Code LFCritical severityair-to-water

Flow sensor fault

Possible causes

Flow sensor disconnected or poorly connected

Affected models: Ecodan Hydrobox, Ecodan All-in-One, EHPX

This issue requires a qualified technician. Do not open the unit.

Code LLCritical severityair-to-water

Installation type setting error

Possible causes

Installation type incorrectly configured (1 zone / 2 zones / tank)
Configuration jumpers incorrectly positioned
Board replaced without reconfiguration

What you can check

Technician intervention required for reconfiguration

Affected models: Ecodan Hydrobox, Ecodan All-in-One, EHPX

This issue requires a qualified technician. Do not open the unit.

Circuit board — Mitsubishi Electric

A control or power board is no longer responding. A full restart sometimes clears a false fault; otherwise, the board needs to be replaced.

Code E34Informationair-to-water

Outdoor unit PCB power supply fault

Affected models: Yack Modul’O

Code E51Informationair-to-water

Inverter PCB fault

Affected models: Yack Modul’O

This issue requires a qualified technician. Do not open the unit.

Code LACritical severityair-to-water

Pressure sensor fault

Possible causes

Connector disconnected
Loose wiring
Faulty sensor
Faulty FTC board

Affected models: Ecodan Hydrobox, Ecodan All-in-One, EHPX, ERSC

This issue requires a qualified technician. Do not open the unit.

Code LBCritical severityair-to-water

High pressure protection

Possible causes

Reduced heating circuit flow
Clogged plate heat exchanger
Outdoor unit fault

Affected models: Ecodan Hydrobox, Ecodan All-in-One, EHPX

This fault requires a qualified technician. Do not open the unit.

Compressor — Mitsubishi Electric

The compressor is the main and most expensive part. These codes protect the unit by shutting it down before damage occurs: never force repeated restarts.

Code E55Informationair-to-water

Compressor shell temperature sensor fault

Affected models: Yack Modul’O

This fault requires a qualified technician. Do not open the unit.

Code E59Informationair-to-water

Compressor start-up error

Affected models: Yack Modul’O

This fault requires a qualified technician. Do not open the unit.

Code E60Informationair-to-water

Compressor charge position detection error

Affected models: Yack Modul’O

This fault requires a qualified technician. Do not open the unit.

Code P5Critical severityair-to-air

Condensate pump fault

Possible causes

Condensate pump failure
Clogged condensate drain

Affected models: MUZ-AP, MUZ-AY, MUZ-LN

This fault requires a qualified technician. Do not open the unit.

Power module — Mitsubishi Electric

Code E41Informationair-to-water

Power transistor overheating

Affected models: Yack Modul’O

This fault requires a qualified technician. Do not open the unit.

Code P2Medium severityair-to-air

Liquid pipe sensor fault (TH2)

Possible causes

TH2 thermistor open or short-circuited

Affected models: MUZ-AP, MUZ-AY, MUZ-LN

This fault requires a qualified technician. Do not open the unit.

Code P4Critical severityair-to-air

Condensate sensor fault (float / open connector)

Possible causes

Float connector disconnected
Faulty condensate sensor

Affected models: MUZ-AP, MUZ-AY, MUZ-LN

This fault requires a qualified technician. Do not open the unit.

Code P6Critical severityair-to-air

Indoor coil freeze (cold) / overheat (heat) protection

Possible causes

Reduced airflow (dirty filter, fan issue)

Affected models: MUZ-AP, MUZ-AY, MUZ-LN

This fault requires a qualified technician. Do not open the unit.

Discharge temperature — Mitsubishi Electric

The compressor outlet temperature exceeds the safety threshold. This points to low refrigerant charge or degraded heat exchange.

Code E36Informationair-to-water

Abnormal discharge temperature

Affected models: Yack Modul’O

Code E39Informationair-to-water

Discharge thermistor fault

Affected models: Yack Modul’O

Code EdCritical severityair-to-air

Serial communication error (outdoor control board / M-NET board)

Possible causes

Communication between the outdoor board and the M-NET board is not possible

Affected models: MUZ-AP, MUZ-AY, MUZ-LN

This fault requires a qualified technician. Do not open the unit.

Code U3Critical severityair-to-air

Compressor discharge temperature sensor fault

Possible causes

Faulty discharge thermistor
Actual compressor overheating
Refrigerant leak

What you can check

Turn off the power — do not restart before diagnosis

Affected models: MUZ-AP, MUZ-AY, MUZ-LN

This fault requires a qualified technician. Do not open the unit.

Low pressure — Mitsubishi Electric

Refrigerant circuit pressure is too low. This often indicates a lack of refrigerant, meaning a leak needs to be found.

Code E49Informationair-to-water

LP (low pressure) fault

Affected models: Yack Modul’O

This fault requires a qualified technician. Do not open the unit.

Code E57Informationair-to-water

Low refrigerant charge

Affected models: Yack Modul’O

This fault requires a qualified technician. Do not open the unit.

Code U2Critical severityair-to-air

Abnormally high discharge temperature (49C) / refrigerant shortage

Possible causes

Refrigerant shortage
Compressor overheating

Affected models: MUZ-AP, MUZ-AY, MUZ-LN

This fault requires a qualified technician. Do not open the unit.

Power supply — Mitsubishi Electric

The supply voltage is abnormal or absent. Check the dedicated circuit breaker first.

Code E47Informationair-to-water

Inverter overvoltage (FDCVA251)

Affected models: Yack Modul’O

This fault requires a qualified technician. Do not open the unit.

Code LCMedium severityair-to-water

Boiler circuit water overheat protection (boiler backup heater)

Possible causes

Boiler setpoint temperature too high
Reduced heating circuit flow

Affected models: Ecodan, Ecodan Hydrobox, PUHZ, EHPX

Communication — Mitsubishi Electric

The indoor and outdoor units are no longer communicating. It’s often the connecting cable or a circuit board, not the refrigerant circuit.

Code E45Informationair-to-water

Inverter PCB communication fault

Affected models: Yack Modul’O

This fault requires a qualified technician. Do not open the unit.

Code U4Medium severityair-to-air

Outdoor unit sensors open or short-circuited (TH3, TH6, TH7, TH8)

Possible causes

Faulty outdoor thermistor
Connection

Affected models: MXZ, MSZ multi-split

This fault requires a qualified technician. Do not open the unit.

Fan — Mitsubishi Electric

The fan expels or draws in heat. If it’s blocked or faulty, pressure rises and triggers a shutdown.

Code E48Informationair-to-water

DC fan motor fault

Affected models: Yack Modul’O

Code U8Medium severityair-to-water

Outdoor fan malfunction

Possible causes

Fan blocked by frost or a foreign object
Faulty fan motor
Fan power board failure

What you can check

Turn off the power and check that nothing is blocking the blade
Defrost the blade if it’s frozen
Clear the area around the unit

Affected models: Ecodan, Ecodan Zubadan, PUHZ, PUD

This fault requires a qualified technician. Do not open the unit.

Defrosting — Mitsubishi Electric

The defrost cycle doesn’t complete properly. This is common in winter and made worse by a clogged drain under the outdoor unit.

Code LHCritical severityair-to-water

Boiler circuit water freeze protection

Possible causes

Leak
Clogged filter
Faulty circulator pump

Affected models: Ecodan, Ecodan Hydrobox, PUHZ, EHPX

This fault requires a qualified technician. Do not open the unit.

High pressure — Mitsubishi Electric

The refrigerant circuit pressure is too high. This is a safety feature: the unit shuts off before the compressor gets damaged.

Code U1Critical severityair-to-air

High pressure fault (HP sensor protection)

Possible causes

Excessive high pressure
Dirty condenser
Refrigerant overcharge

What you can check

Clean the condenser
Check the outdoor unit’s ventilation

Affected models: MUZ-AP, MUZ-AY, MUZ-LN

This fault requires a qualified technician. Do not open the unit.

Reversing valve — Mitsubishi Electric

Code E32Informationair-to-water

Phase reversal or phase not connected

Affected models: Yack Modul’O

All Mitsubishi Electric codes published on the site

This list updates itself automatically with each new guide.

Technical information provided for guidance only, based on manufacturer documentation and field feedback. It does not replace the diagnosis of a qualified professional. Found an error on this page? Report it.