A Daikin error code is a two-character code that tells you which part of the system has stopped it. The ones people see most are U4, a communication fault between the indoor and outdoor units, A5, which Daikin lists as high pressure control in heating or freeze-up protection in cooling and links to a clogged indoor air filter, A3, a drain fault, E7, an outdoor fan motor fault, and U0, a shortage of refrigerant.
The letter tells you the area, the second character the specific fault. Every code and cause on this page comes from Daikin's own Simple Self-Diagnosis by Malfunction Code chart, which covers Daikin residential, Sky Air and VRV air conditioning. Codes we could not find in Daikin's documents are not included.
At a glance
| Question | Answer |
|---|---|
| Indoor and outdoor unit not communicating | U4 |
| Filter or indoor coil related | A5, which Daikin links to a clogged indoor air filter or a heat exchanger thermistor fault |
| Water or drain problem | A3, drain level control system abnormality |
| Outdoor fan problem | E7 (fan motor system) or H7 (fan motor signal) |
| Refrigerant or pressure problem | U0 (shortage of refrigerant), E3 (high pressure switch), E4 (low pressure switch), F3, F6 |
| Power supply problem | U2 (power supply or instantaneous power failure), U1 (reverse or open phase), A8 |
| Circuit board | A1 (indoor PCB), E1 (outdoor PCB), L1 (inverter PCB) |
| How to read the code | On most wireless remotes, hold TIMER CANCEL for about 5 seconds, then press it repeatedly until you hear a continuous beep |
Source: Daikin, Simple Self-Diagnosis by Malfunction Code (SM-TS3), and Daikin's remote controller self-diagnosis instructions.
How Daikin error codes are organised
Daikin groups its codes by where the fault is. A and C codes come from the indoor unit and its sensors. E, F, H and J codes come from the outdoor unit: its protection devices, refrigerant temperatures and pressures, and its sensors. L codes are the inverter, P codes the power supply and outdoor unit settings, and U codes the system as a whole, including wiring and communication between units. M codes relate to central controllers on larger systems.
Not every code applies to every unit. Daikin's chart marks which product families each code applies to, across residential units, Sky Air, VRV, packaged and heat reclaim ventilation equipment. A code that appears only on VRV systems will not show on a single wall unit.
How to read the code on your remote
Wireless remotes on wall-mounted units
Many Daikin wireless remotes find the code by trial. Daikin's instructions are to hold the TIMER CANCEL button (ON TIMER CANCEL or OFF TIMER CANCEL on some remotes) for 5 seconds until "00" flashes in the temperature display, then press the same button repeatedly. The display steps through the codes, and a continuous beep tells you the code on screen is the one the unit has stored.
Daikin's operation manual for the ARC452A series adds that a short beep or two short beeps mean the displayed code does not match. To leave this mode, hold the button for 5 seconds again, or leave it for a minute and it cancels itself.
Wired remotes
Daikin's self-diagnosis guide for Sky Air and VRV describes the wired controllers. With a BRC1E62, the operation indicator blinks and the screen shows "Error: Press Menu Button", and pressing Menu/Enter displays the malfunction code. A BRC1C62 blinks its operation LED and shows the code on its display. Wireless remotes for Sky Air and VRV systems find the code through the INSPECTION/TEST button, with beeps confirming each digit.
Daikin error code lookup
Type the code from your remote or display to see what it means and what to do next.
Daikin Error Code Lookup
Type a code (e.g. U4, E3, A3) or a keyword like fan or thermistor. Built from Daikin service data and 20 years of London callouts.
A0External protection device activatedService soon
An external protection device connected to terminals T1 and T2 on the indoor unit has activated.
- Check whether any external safety device wired to the indoor unit has tripped.
- Reset the unit once at the isolator.
- If A0 returns, call an engineer. Never bypass a safety device.
A1Malfunction of indoor unit PCBStop and call an engineer
Daikin lists a defective indoor unit PCB, or an external factor such as electrical noise, as the causes.
- Switch off at the isolator for 5 minutes, then restart.
- If A1 returns, the indoor PCB needs testing by an engineer.
A3Drain level control system abnormalityService soon
The drain system has a problem. Daikin lists a clogged drain or one with an upward slope, a defective drain pump, or a defective float switch.
- Switch the unit off and look for water at the indoor unit.
- Do not keep restarting it, or condensate can overflow.
- Have the drain, pump and float switch checked by an engineer.
A5High pressure control in heating, freeze-up protection in coolingService soon
Protection against high pressure in heating mode, or against the indoor coil freezing in cooling mode. Daikin lists a clogged indoor air filter, a short circuit of air, or a defective indoor heat exchanger thermistor.
- Clean the indoor air filters.
- Make sure nothing is blocking the indoor unit's air inlet or outlet.
- If A5 returns with clean filters, call an engineer.
A6Malfunction of indoor fan motorStop and call an engineer
Daikin lists broken wires, a short circuit or loose connectors in the fan motor harness, a defective fan motor, or a defective indoor unit PCB.
- Switch off at the isolator.
- Call an engineer to test the fan motor, its wiring and the indoor PCB.
A7Malfunction of swing flap motorInformation
Daikin lists a defective swing flap motor, indoor unit PCB or connection cable, or a defective airflow direction flap cam.
- Check nothing is jamming the louvre.
- The flap motor or its wiring needs an engineer if the code returns.
A9Malfunction of electronic expansion valveStop and call an engineer
Daikin lists a defective electronic expansion valve coil, a defective indoor unit PCB, or defective relay cables.
- Switch the unit off.
- This is an engineer job: the valve coil, cables and PCB need testing.
AHMalfunction of dust collector of air cleanerInformation
Daikin lists a defective dust collecting element, a stained insulator, a defective high voltage power supply unit, or a defective indoor unit PCB.
- Clean the air cleaner parts as the user manual describes.
- If AH returns, the air cleaner unit needs an engineer.
C4Malfunction of heat exchanger liquid pipe thermistorService soon
Daikin lists a defective liquid pipe thermistor, a defective indoor unit PCB, or a defective connector contact.
- Reset the unit once at the isolator.
- If C4 returns, an engineer needs to test the thermistor and its connector.
C5Malfunction of heat exchanger gas pipe thermistorService soon
Daikin lists a defective gas pipe thermistor, a defective indoor unit PCB, or a defective connector contact.
- Reset the unit once at the isolator.
- If C5 returns, an engineer needs to test the thermistor and its connector.
C7Front panel driving motor faultInformation
Daikin lists a defective front panel driving motor or a defective limit switch.
- Check nothing is stopping the front panel from opening or closing.
- If C7 returns, the panel motor or limit switch needs an engineer.
C9Malfunction of suction air thermistorService soon
Daikin lists a defective suction air thermistor, a defective indoor unit PCB, or a defective connector contact.
- Reset the unit once at the isolator.
- If C9 returns, an engineer needs to test the thermistor and its connector.
CCMalfunction of humidity sensor systemInformation
Daikin lists a defective humidity sensor or a defective connector contact.
- Reset the unit once at the isolator.
- If CC returns, an engineer can test the sensor and its connector.
E0Protection devices activated (unified)Stop and call an engineer
A protection device connected to the outdoor unit PCB has activated, or a protection device connector has a poor contact.
- Switch the system off.
- Do not keep resetting it. Call an engineer to find which protection device tripped and why.
E1Defective outdoor unit PCBStop and call an engineer
Daikin lists a defective outdoor unit PCB, or a defective connection of the relay wires between the units.
- Switch off at the isolator for 10 minutes, then restart.
- If E1 returns, the outdoor PCB and wiring need an engineer.
E3Actuation of high pressure switchStop and call an engineer
The high pressure switch has tripped. Daikin lists a dirty outdoor heat exchanger, a defective high pressure switch, clogged refrigerant piping, or a defective connector contact.
- Switch the system off.
- Check nothing is blocking the outdoor unit, such as leaves, covers or stored items.
- Call an F gas qualified engineer if E3 returns.
E4Actuation of low pressure switchStop and call an engineer
Daikin lists an abnormal drop in low pressure, a defective low pressure sensor, a defective outdoor unit PCB, or a defective connector contact.
- Switch the system off.
- Low pressure can point to a refrigerant shortage, so call an F gas qualified engineer.
E5Inverter compressor motor lock or overheatStop and call an engineer
Inverter compressor motor overheat, compressor lock or high differential pressure. Daikin lists a defective inverter PCB, a UVW connection error, or a defective connector contact.
- Switch off at the isolator and let the unit rest.
- If E5 returns, the compressor and inverter need an engineer.
E6STD compressor motor overcurrent or lockStop and call an engineer
Daikin lists a defective compressor, a defective control PCB, or a stop valve that has not been opened. On some multi-system units, E6 is compressor overcurrent, with a defective expansion valve or a refrigerant shortage among the causes.
- Switch the system off.
- On a new installation, the stop valves need checking first.
- Call an engineer to test the compressor and control board.
E7Malfunction of outdoor unit fan motorStop and call an engineer
Daikin lists a missing or defective connection between the fan motor and the PCB, or a fan that cannot turn because something is caught in it.
- Switch off at the isolator.
- Check whether anything is caught in the outdoor fan, without putting hands inside.
- Call an engineer if E7 returns.
E8Overcurrent of inverter compressorStop and call an engineer
Daikin lists a defective compressor, a defective inverter main circuit capacitor, a defective outdoor unit PCB, or a defective power transistor.
- Switch the system off.
- This needs an engineer to test the compressor and inverter.
E9Malfunction of electronic expansion valve coilStop and call an engineer
Daikin lists disconnected expansion valve connectors, a defective expansion valve coil, or a defective outdoor unit control PCB.
- Switch the system off.
- The valve coil and its connectors need an engineer.
EAMalfunction of four way valve or cool/heat switchingService soon
Daikin lists a defective four way valve, a shortage of gas, a defective outdoor unit PCB, or a defective thermistor.
- Note which mode the unit was in when EA appeared.
- Call an engineer to test the four way valve and refrigerant charge.
F3Malfunction of discharge pipe temperatureStop and call an engineer
Daikin lists a defective discharge pipe thermistor, an abnormal discharge pipe temperature, a defective outdoor unit control PCB, or a defective connector contact.
- Switch the system off and let it rest.
- A high discharge temperature can point to a refrigerant problem, so call an F gas qualified engineer.
F6Abnormal high pressure or refrigerant overchargedService soon
Daikin lists an overcharge of refrigerant, or a disconnected heat exchanger deicer, outdoor air or liquid pipe thermistor, or a defective outdoor unit PCB.
- Switch the system off.
- Call an F gas qualified engineer, especially if the system was recently charged or serviced.
H0Malfunction of compressor sensor systemStop and call an engineer
Daikin lists a disconnected or poorly connected harness, or a defective PCB.
- Switch the system off.
- This needs an engineer to check the harness and PCB.
H3Malfunction of high pressure switchService soon
A fault with the high pressure switch itself, rather than a trip. Daikin lists a defective high pressure switch, a broken wire, a defective outdoor unit PCB, or a defective connector contact.
- Reset the unit once at the isolator.
- If H3 returns, an engineer needs to test the switch and its wiring.
H6Malfunction of position detection sensorStop and call an engineer
Daikin lists a faulty contact of the compressor cable, a defective compressor, or a defective outdoor unit PCB.
- Switch the system off.
- This needs an engineer to test the compressor cable, compressor and PCB.
H7Malfunction of outdoor unit fan motor signalStop and call an engineer
An abnormal signal from the fan motor. Daikin lists a circuit failure, a disconnection or short circuit in the fan motor leads, or a defective inverter PCB.
- Switch off at the isolator.
- Call an engineer to test the fan motor and its leads.
H8Malfunction of compressor input (CT) systemStop and call an engineer
Daikin lists a defective power transistor, a defective reactor, faulty inverter wiring, or a defective outdoor unit PCB.
- Switch the system off.
- This needs an engineer to test the inverter circuit.
H9Malfunction of outdoor air thermistorService soon
Daikin lists a defective thermistor connection, a defective outdoor unit PCB, or a defective outdoor air thermistor.
- Reset the unit once at the isolator.
- If H9 returns, an engineer needs to test the thermistor and its connection.
J3Malfunction of discharge pipe thermistorService soon
Daikin lists a defective thermistor connection, a defective discharge pipe thermistor, or a defective outdoor unit PCB.
- Reset the unit once at the isolator.
- If J3 returns, an engineer needs to test the thermistor and its connection.
J5Malfunction of suction pipe thermistorService soon
Daikin lists a defective thermistor connection, a defective suction pipe thermistor, or a defective outdoor unit PCB.
- Reset the unit once at the isolator.
- If J5 returns, an engineer needs to test the thermistor and its connection.
J6Malfunction of heat exchanger thermistorService soon
Daikin lists a defective thermistor connection, a defective heat exchanger thermistor, or a defective outdoor unit PCB.
- Reset the unit once at the isolator.
- If J6 returns, an engineer needs to test the thermistor and its connection.
L3Electrical component box temperature riseStop and call an engineer
Daikin lists a fin temperature rise caused by a short circuit of air, a defective outdoor unit fan motor, a defective power transistor, or a defective outdoor unit PCB.
- Check nothing is blocking airflow around the outdoor unit.
- Call an engineer if L3 returns.
L4Inverter radiation fin temperature riseStop and call an engineer
Daikin lists a fin temperature rise caused by a short circuit of air, or a defective fin thermistor.
- Check nothing is blocking airflow around the outdoor unit.
- Call an engineer if L4 returns.
L5Inverter instantaneous overcurrent (DC output)Stop and call an engineer
Daikin lists a defective compressor coil, such as a wiring disconnection or insulation failure, a compressor start-up failure from a mechanical lock, or a defective inverter PCB.
- Switch the system off.
- This needs an engineer to test the compressor and inverter.
L8Overcurrent of inverter compressorStop and call an engineer
The inverter compressor is overloaded. Daikin lists a wiring disconnection in the compressor coil, disconnected compressor wiring, or a defective inverter PCB.
- Switch the system off and let it rest.
- If L8 returns, call an engineer.
L9Inverter compressor start-up error (stall prevention)Stop and call an engineer
Daikin lists a stop valve that has not been opened, a defective compressor, an error in the compressor wiring, a large pressure difference before start-up, or a defective inverter PCB.
- Switch the system off.
- On a new installation, the stop valves need checking first.
- Call an engineer if L9 returns.
P4Malfunction of radiation fin temperature sensorService soon
Daikin lists a defective radiation fin thermistor, a defective inverter PCB, a defective inverter compressor, or a defective fan motor.
- Reset the unit once at the isolator.
- If P4 returns, call an engineer.
PJMalfunction of capacity settingService soon
The capacity setting on the outdoor unit PCB is wrong or missing. Daikin lists an improper or missing capacity setting adaptor, a PCB type mismatch, or no field setting made after the outdoor PCB was replaced.
- PJ usually follows a board replacement or a new installation.
- The engineer who fitted the board needs to complete the setting.
U0Shortage of refrigerantStop and call an engineer
Daikin lists a refrigerant shortage or blockage, a defective thermistor, a defective low pressure sensor, or a defective outdoor unit main PCB.
- Switch the system off.
- A refrigerant shortage means a leak to find and repair, which needs an F gas qualified engineer.
U2Malfunction of power supply or instantaneous power failureStop and call an engineer
Daikin lists an abnormal power supply voltage, an instantaneous power failure, or defective main circuit wiring.
- Check whether there has been a power cut or a tripped breaker.
- If U2 returns with a steady supply, call an engineer to check the supply and wiring.
U4Transmission error between indoor and outdoor unitStop and call an engineer
Daikin lists a short circuit or wrong wiring in the indoor to outdoor transmission wiring (F1/F2), the outdoor unit power being off, a system address mismatch, or a defective indoor or outdoor unit PCB.
- Check the outdoor unit has power at its isolator and breaker.
- If it does, call an engineer to check the wiring and boards.
U5Transmission error between indoor unit and remote controllerStop and call an engineer
Daikin lists a transmission error, two remote controllers both set as main, a defective indoor unit or remote controller PCB, or electrical noise.
- Reset the unit once at the isolator.
- If two remote controllers are fitted, one should be set as main and one as sub.
- Call an engineer if U5 returns.
U7Transmission error between outdoor unitsStop and call an engineer
On multi-outdoor systems, a transmission fault between outdoor units or with an external control adaptor. Daikin lists wiring connection errors or a defective outdoor unit PCB.
- This needs an engineer to check the transmission wiring between the outdoor units.
U8Transmission error between remote controllersService soon
Daikin lists a transmission error between the main and sub remote controllers, a connection between two sub controllers, or a defective remote controller PCB.
- Check how the remote controllers are set up: one main, one sub.
- Call an engineer if U8 returns.
UAImproper combination of indoor and outdoor unitsStop and call an engineer
Daikin lists wrong model connections, too many indoor units, mismatched refrigerant types, an improper power supply, a wrong or defective PCB, or a setting not made after a spare PCB was fitted.
- UA usually appears on a new installation or after a repair.
- The installing engineer needs to check the combination and settings.
UFSystem is not set yetStop and call an engineer
Daikin lists improper transmission wiring between the units, a check operation that has not been run, a defective indoor unit PCB, or a stop valve that has not been opened.
- UF usually appears on a new installation.
- The installing engineer needs to complete the wiring checks and test run.
Got a code that needs an engineer? Be Cool covers all London postcodes.
Call 0203 488 1889Daikin error code list
These are the codes from Daikin's chart for split, multi-split, Sky Air and VRV air conditioning. The meaning and causes are given in Daikin's own words. Codes that apply only to chillers, thermal storage units and automatic refrigerant charging have been left out.
A codes: indoor unit
| Code | What Daikin says it means | Causes Daikin lists |
|---|---|---|
| A0 | External protection device activated | External protection device connected to the terminal strip T1-T2 of indoor unit is activated |
| A1 | Malfunction of indoor unit PCB | Defective indoor unit PCB; External factor (Noise etc.) |
| A3 | Drain level control system abnormality | Drain clogging, upward slope, etc.; Defective drain pump; Defective float switch or short circuit connector |
| A5 | High pressure control in heating, freeze-up protection control in cooling | Clogged air filter of indoor unit and short circuit; Defect of indoor unit heat exchanger thermistor |
| A6 | Malfunction of fan motor | Broken wires in, short circuit of, or disconnection of connectors from the fan motor harness; Defective fan motor; Defective indoor unit PCB |
| A7 | Malfunction of swing flap motor | Defective swing flap motor; Defective indoor unit PCB; Defective connection cable; Defective airflow direction adjusting flap-cam |
| A8 | Malfunction of power supply or AC input overcurrent | Defective power supply voltage; Defective connection on signal line; Defective wiring |
| A9 | Malfunction of electronic expansion valve | Defective electronic expansion valve coil; Defective indoor unit PCB; Defective relay cables |
| AF | Malfunction of a humidifier system | Humidifier unit (optional accessory) leaking; Defective drain piping (upward slope, etc.); Defective indoor unit PCB |
| AH | Malfunction of dust collector of air cleaner | Defect of dust collecting element; Stained insulator part; Defect of high voltage power supply unit; Defect of indoor unit PCB |
| AJ | Malfunction of capacity setting (indoor unit PCB) | The capacity setting adaptor was not installed when replacing PCB; Defective indoor unit PCB |
C codes: indoor unit sensors
| Code | What Daikin says it means | Causes Daikin lists |
|---|---|---|
| C1 | Failure of transmission (between indoor unit PCB and sub PCB) | Defective connection of the connector between indoor unit PCB |
| C4 | Malfunction of liquid pipe thermistor for heat exchanger | Defective thermistor for liquid pipe; Defective indoor unit PCB; Defective connector contact |
| C5 | Malfunction of gas pipe thermistor for heat exchanger | Defective thermistor for gas pipe; Defective indoor unit PCB; Defective connector contact |
| C6 | Malfunction of fan motor sensor or fan control driver | Defective fan PCB; Defective connection of capacity setting adaptor; Field setting error |
| C7 | Front panel driving motor fault | Defective front panel driving motor; Defective limit switch |
| C9 | Malfunction of suction air thermistor | Defective thermistor for suction air; Defective indoor unit PCB; Defective connector contact |
| CA | Malfunction of discharge air thermistor | Defective thermistor for discharge air; Defective indoor unit PCB; Defective connector contact |
| CC | Malfunction of humidity sensor system | Defective humidity sensor; Defective connector contact |
| CJ | Room temperature thermistor in remote controller abnormality | Defective room temperature thermistor in remote controller; Defective remote controller PCB; External factor (Noise etc.) |
E codes: outdoor unit protection
| Code | What Daikin says it means | Causes Daikin lists |
|---|---|---|
| E0 | Protection devices activated (unified) | Protection device connected to outdoor unit PCB actuated; Defective protection device connector contact |
| E1 | Defective outdoor unit PCB | Defective outdoor unit PCB; Defective connection of inside/ outside relay wires |
| E3 | Actuation of high pressure switch (HPS) | Dirty outdoor unit heat exchanger; Defective high pressure switch; Clogged refrigerant piping; Defective connector contact |
| E4 | Actuation of low pressure switch (LPS) | Abnormally drop in low pressure; Defective low pressure sensor; Defective outdoor unit PCB; Defective connector contact |
| E5 | Inverter compressor motor lock or overheat | Inverter compressor lock; High differential pressure; Defective inverter PCB; UVW connection error; Defective connector contact |
| E6 | STD compressor motor overcurrent/lock | Defective compressor; Defective control PCB; The stop valve is not opened |
| E7 | Malfunction of outdoor unit fan motor system | Fan motor failure; Neglect to connect or defective connection of harness/connector between the fan motor and the PCB; Fan does not rotate due to foreign matters caught in it |
| E8 | Overcurrent of inverter compressor | Defective compressor; Defective inverter main circuit capacitor; Defect of outdoor unit PCB; Defect of power transistor |
| E9 | Malfunction of electronic expansion valve coil | Disconnection of connectors from electronic expansion valves; Defective electronic expansion valve coil; Defective outdoor unit control PCB |
| EA | Malfunction of four way valve or cool/heat switching | Defective four way valve; Shortage of gas; Defective outdoor unit PCB; Defective thermistor |
F codes: refrigerant circuit temperature and pressure
| Code | What Daikin says it means | Causes Daikin lists |
|---|---|---|
| F3 | Malfunction of discharge pipe temperature | Defective discharge pipe thermistor; Abnormal discharge pipe temperature; Defective outdoor unit control PCB; Defective connector contact |
| F6 | Abnormal high pressure or refrigerant overcharged | Refrigerant overcharged; Disconnection of heat exchanger deicer thermistor; Disconnection of outdoor air thermistor; Disconnection of liquid pipe temperature thermistor; Defective outdoor unit PCB |
H codes: outdoor unit sensors
| Code | What Daikin says it means | Causes Daikin lists |
|---|---|---|
| H0 | Malfunction of sensor system of compressor | Harness is disconnected, or defective connection; Defective PCB |
| H1 | Malfunction of room temperature sensor or humidifier unit damper | Defective limit switch; Defective damper |
| H3 | Malfunction of high pressure switch (HPS) | Defective high pressure switch; Broken wire; Defective outdoor unit PCB; Defective connector contact |
| H4 | Malfunction of low pressure switch (LPS) | Defective low pressure switch; Broken wire; Defective outdoor unit PCB; Defective connector contact |
| H5 | Malfunction of compressor motor overload thermistor | Defect of compressor motor overload thermistor; Defective connector contact |
| H6 | Malfunction of position detection sensor | Faulty contact of compressor cable; Defective compressor; Defective outdoor unit PCB |
| H7 | Malfunction of outdoor unit fan motor signal | Abnormal signal from fan motor (Circuit failure); Disconnection/Short circuit in fan motor leads or disconnection of connector; Defective inverter PCB |
| H8 | Malfunction of compressor input (CT) system | Defective power transistor; Defective reactor; Faulty wiring of inverter system; Defective outdoor unit PCB |
| H9 | Malfunction of outdoor air thermistor | Defective connection of thermistor; Defective outdoor unit PCB; Defective outdoor air thermistor |
J codes: outdoor unit thermistors and pressure sensors
| Code | What Daikin says it means | Causes Daikin lists |
|---|---|---|
| J1 | Malfunction of pressure sensor | Defective pressure sensor connector contact; Defective pressure sensor; Defective outdoor unit PCB |
| J2 | Malfunction of current sensor of compressor | Defective current sensor; Defective compressor; Defective outdoor unit PCB |
| J3 | Malfunction of discharge pipe thermistor | Defective connection of thermistor; Defective discharge pipe thermistor; Defective outdoor unit PCB |
| J4 | Malfunction of low pressure equivalent saturated temperature sensor system | Defective connection of thermistor; Defective thermistor; Defective outdoor unit PCB |
| J5 | Malfunction of suction pipe thermistor | Defective connection of thermistor; Defective suction pipe thermistor; Defective outdoor unit PCB |
| J6 | Malfunction of heat exchanger thermistor | Defective connection of thermistor; Defective heat exchanger thermistor; Defective outdoor unit PCB |
| J7 | Malfunction of thermistor (Refrigerant circuit) | Defective connection of thermistor; Defective liquid pipe thermistor; Defective outdoor unit PCB |
| J8 | Malfunction of thermistor (Refrigerant circuit) | Defective connection of thermistor; Defective liquid pipe thermistor; Defective outdoor unit PCB |
| J9 | Malfunction of thermistor (Refrigerant circuit) | Defective connection of thermistor; Defective gas pipe thermistor; Defective outdoor unit PCB |
| JA | Malfunction of high pressure sensor | Defective connector contact; Connection of low pressure sensor in mistake for high pressure sensor; Defective high pressure sensor; Defective outdoor unit PCB |
| JC | Malfunction of low pressure sensor | Defective connector contact; Connection of high pressure sensor in mistake for low pressure sensor; Defective low pressure sensor; Defective outdoor unit PCB |
L codes: inverter system
| Code | What Daikin says it means | Causes Daikin lists |
|---|---|---|
| L0 | Malfunction of inverter system | Shortage of power supply capacity; Defective power transistor; Defective outdoor unit PCB |
| L1 | Malfunction of inverter PCB | Defective compressor wiring; Defective outdoor unit fan motor; Blown fuse; Defective inverter PCB |
| L3 | Electrical component box temperature rise | Fin temperature rise due to short circuit; Defective outdoor unit fan motor; Defective power transistor; Defective outdoor unit PCB |
| L4 | Malfunction of inverter radiation fin temperature rise | Fin temperature rise due to short circuit; Defective fin thermistor |
| L5 | Inverter instantaneous overcurrent (DC output) | Defective compressor coil (such as wiring disconnection or insulation failure); Compressor startup failure (mechanical lock); Defective inverter PCB |
| L8 | Malfunction of overcurrent of inverter compressor (compressor overloaded) | Wiring disconnection in compressor coil; Disconnection of compressor wiring; Defective inverter PCB |
| L9 | Malfunction of inverter compressor startup error (stall prevention) | The stop valve is not opened; Defective compressor; Error in wire connections to compressor; Large differential pressure before compressor startup; Defective inverter PCB |
| LA | Malfunction of power transistor | Defective power transistor; Defective compressor; Defective inverter PCB |
| LC | Malfunction of transmission between control and inverter PCB | Defective connection between the inverter PCB and the control PCB; External factors (e.g. noise); Defective inverter compressor; Defective control PCB (transmission block) |
P codes: power supply and outdoor unit settings
| Code | What Daikin says it means | Causes Daikin lists |
|---|---|---|
| P1 | Power voltage imbalance or inverter PCB | Open phase; Interphase voltage imbalance; Defective capacitor in the main circuit; Defective wiring in the main circuit; Defective inverter PCB |
| P3 | Malfunction of thermistor in switch box | Defective connection of thermistor; Defective reactor thermistor; Defective inverter PCB |
| P4 | Malfunction of radiation fin temperature sensor | Defective radiation fin temperature thermistor; Defective inverter PCB; Defective INV. compressor; Defective fan motor |
| PJ | Malfunction of capacity setting (outdoor unit PCB), or improper combination between inverter and fan driver | Capacity setting adaptor is not installed; Improper capacity setting adaptor; Mis-matching of type of PCB; Improper (or no) field setting after replacing outdoor unit main PCB; Defective outdoor unit PCB |
U codes: system, wiring and communication
| Code | What Daikin says it means | Causes Daikin lists |
|---|---|---|
| U0 | Shortage of refrigerant | Refrigerant shortage and refrigerant clogging (wrong piping); Defective thermistor; Defective low pressure sensor; Defective outdoor unit main PCB |
| U1 | Reverse phase, open phase | Power supply reverse phase T phase open phase; Defective outdoor unit PCB (A1P) |
| U2 | Malfunction of power supply or instantaneous power failure | Abnormal power supply voltage; Instantaneous power failure; Defective main circuit wiring |
| U3 | Check operation not executed or transmission error | Check operation is not executed. |
| U4 | Malfunction of transmission between indoor and outdoor unit | Short circuit in indoor-outdoor or outdoor-outdoor transmission wiring (F1/F2), or wrong wiring; Outdoor unit power supply is OFF; System address does not match; Defective indoor unit PCB; Defective outdoor unit PCB |
| U5 | Malfunction of transmission between indoor unit and remote controller | Transmission error between indoor unit and remote controller; Connection of 2 main remote controllers (when using 2 remote controllers); Defective indoor unit PCB; Defective remote controller PCB; Transmission error caused by noise |
| U6 | Malfunction of transmission between indoor units | Faulty wiring; External factor (Noise etc.); Defective indoor unit PCB |
| U7 | Malfunction of transmission between outdoor units or outdoor storage unit | Connection error of transmission wirings between outdoor unit and external control adaptor for outdoor unit; Connection error of transmission wirings between outdoor units; Defective outdoor unit PCB |
| U8 | Malfunction of transmission between remote controllers | Transmission error between main and sub remote controller; Connection between sub remote controllers; Defective remote controller PCB |
| U9 | Malfunction of transmission (other system) | Transmission error between other indoor and outdoor units; Defective electronic expansion valve of other indoor unit; Defective indoor unit PCB of other indoor unit; Improper connection of transmission wiring between indoor and outdoor unit |
| UA | Improper combination of indoor and outdoor units, or indoor/outdoor power supply defect | Wrong model connections; Improper power supply; Excess of connected indoor units; Mismatch of the refrigerant type of indoor and outdoor unit; Setting of outdoor unit PCB was not carried out after replacing to spare PCB; Defective PCB |
| UC | Malfunction of setting of centralized control equipment address | Address duplication of centralized control equipment; Defective indoor unit PCB |
| UE | Malfunction of transmission between indoor unit and centralized control equipment | Transmission error between optional controllers for centralized control equipment and indoor unit; Connector for setting main controller is disconnected; Defective PCB for central remote controller; Defective indoor unit PCB |
| UF | System is not set yet | Improper connection of transmission wiring between indoor-outdoor units and outdoor-outdoor units; Failure to execute check operation; Defective indoor unit PCB; Stop valve is not opened |
| UH | Malfunction of system | Improper connection of transmission wiring between indoor-outdoor units and outdoor-outdoor units; Defective indoor unit PCB; Defective outdoor unit PCB |
| UJ | Malfunction of transmission (accessory device) | Defect of accessory devices; Faulty wiring |
M codes: centralised control
| Code | What Daikin says it means | Causes Daikin lists |
|---|---|---|
| M1 | Malfunction of central remote controller PCB | Defective central remote controller PCB |
| M8 | Malfunction of transmission between optional controllers for centralized control | Other centralized control power disconnection; Centralized control reset switch ON; Defective transmission wiring; Central remote controller address change |
| MA | Improper combination of optional controllers for centralized control | More than one master controller is connected; Faulty setting of centralized control; Defect of centralized control |
| MC | Address duplication, improper setting | Address duplication of central remote controller |
The codes people ask about most
U4: indoor and outdoor units not communicating
Daikin's chart lists the causes as a short circuit or wrong wiring in the transmission wiring between the units, the outdoor unit power supply being off, a system address mismatch, or a defective indoor or outdoor PCB. The one cause an owner can check is the obvious one: whether the outdoor unit has power, for example from its isolator. Anything involving the wiring between the units is a job for an engineer.
A5: high pressure control or freeze-up protection
Daikin describes A5 as high pressure control in heating and freeze-up protection in cooling, and lists a clogged air filter of the indoor unit as a cause, along with a defective indoor heat exchanger thermistor. Clean the filters as the operation manual describes and make sure nothing is blocking the indoor unit's airflow. If A5 comes back with clean filters, the cause is inside the unit.
A3: drain level control system abnormality
The indoor unit has detected that condensate is not draining. Daikin lists drain clogging or an upward slope in the drain pipe, a defective drain pump, and a defective float switch. Stop using the unit in cooling mode, check whether water is dripping from the unit, and have the drain cleared and the pump tested. Our guide to condensate pumps explains how they work and why they fail.
E7: outdoor fan motor system
Daikin's causes include fan motor failure, a poor harness or connector between the fan motor and the PCB, and the fan not rotating "due to foreign matters caught in it". With the power isolated, check from outside the casing that nothing has blown into the fan guard. Do not open the unit.
U0: shortage of refrigerant
Daikin lists refrigerant shortage and clogging, a defective thermistor, a defective low pressure sensor or a defective outdoor main PCB. Refrigerant does not get used up, so a genuine shortage means a leak. Finding and repairing it is work for an F gas certified engineer, and topping up without a repair does not meet the F gas rules. Our guide to air conditioning refrigerants explains which gas your unit is likely to use.
E3 and E4: pressure switches
E3 is the high pressure switch actuating, which Daikin links to a dirty outdoor heat exchanger, a defective switch, clogged refrigerant piping or a poor connection. E4 is the low pressure switch, linked to an abnormal drop in low pressure, a defective sensor or the outdoor PCB. Keep the outdoor unit's coil clear of leaves and debris, but anything on the refrigerant side needs an engineer.
What you can check safely
- Read the code using the remote procedure above and write it down, with any unit number shown.
- Clean the indoor filters following the operation manual, especially for A5.
- Check the outdoor unit has power and that its coil and fan guard are not blocked, for U4, E3 and E7.
- Look for water around the indoor unit for A3.
- Breakers. Daikin warns that if a circuit breaker or earth leakage breaker has tripped, it should not be reset immediately without first checking for problems with the insulation of the equipment.
On wired controllers, Daikin notes that holding ON/OFF for four seconds or more in the malfunction code display clears the malfunction history. Clearing a code does not fix its cause.
When to call an engineer
- Any refrigerant-side code, including U0, E3, E4, F3 and F6. Work on the refrigerant circuit needs the F gas qualifications set out by GOV.UK.
- Any PCB, inverter or power supply code, such as A1, E1, the L codes, U1 and U2.
- A code that comes back after you have cleaned the filters and checked the power.
- Any code alongside a burning smell, unusual noise or water coming from the unit.
When you call, give the engineer the code, the model number from the unit's rating plate, and what the unit was doing when it stopped. It saves a diagnostic visit going in blind.
Daikin Altherma heat pumps
This page covers Daikin air conditioning. Daikin Altherma air-to-water heat pumps have their own error codes, set out in their installer and user manuals, so check the manual for your Altherma model rather than this list.
Questions people ask about Daikin error codes
What does U4 mean on a Daikin air conditioner?
U4 is a malfunction of transmission between the indoor and outdoor unit. Daikin lists causes including wiring faults between the units, the outdoor unit power supply being off, an address mismatch and a defective indoor or outdoor PCB. Check the outdoor unit has power, then call an engineer.
What does A5 mean on a Daikin?
Daikin describes A5 as high pressure control in heating and freeze-up protection in cooling. Its listed causes include a clogged indoor air filter and a defective indoor heat exchanger thermistor, so clean the filters first and call an engineer if the code returns.
What does U0 mean on a Daikin?
U0 is a shortage of refrigerant. Daikin also lists refrigerant clogging, a defective thermistor, a defective low pressure sensor and a defective outdoor main PCB as causes. A genuine shortage means a leak, which needs an F gas certified engineer.
How do I check the error code on a Daikin remote?
On many wireless remotes, hold TIMER CANCEL for 5 seconds until "00" flashes, then press it repeatedly until you hear a continuous beep. The code on the display at that point is the stored fault. On a BRC1E62 wired remote, press Menu/Enter when the screen shows the error message.
How do I reset a Daikin error code?
Clearing the code does not fix the fault behind it. On wired controllers, Daikin says holding ON/OFF for four seconds or more in the malfunction code display clears the history. If a breaker has tripped, Daikin advises checking the equipment's insulation before resetting it.
Are Daikin error codes the same on every model?
The code letters mean the same thing across the range, but not every code exists on every unit. Daikin's chart marks which product families each code applies to, so a VRV-only code will not appear on a single wall unit.
Getting a Daikin fixed properly
A Daikin code tells an engineer where to start, not what to replace. If yours is showing a code that will not clear, our air conditioning repair team works on Daikin systems across London, and regular air conditioning maintenance prevents the filter, drain and coil faults behind many of these codes.
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.