Daikin Mini Split Error Codes: U4, A5, U0 and the Rest

By Ray Bennett · Updated 2 October 2026 · 7 min read · Checked against the maker’s manual

Daikin Mini Split Error Codes: U4, A5, U0 and the Rest

Short answer

A Daikin wall unit blinks its operation lamp when it stops on a fault, and the remote reads the code: hold the timer Cancel button until 00 blinks, then press until a long beep. U4 means the indoor and outdoor units are not talking, A5 is often a clogged filter, U0 is a refrigerant shortage, and E7 is the outdoor fan.

A Daikin wall unit does not show its fault code on the front. It stops and blinks its operation lamp, and the code is read with the remote, which beeps when it lands on the right one. It takes a minute once you know the button.

Everything on this page comes from Daikin Industries’ own documents: its “Simple Self-Diagnosis by Malfunction Code” list and “How to Check Error Codes” guide from the after sales service division, and Daikin’s operation manual for its residential wall units. The meanings and likely causes are Daikin’s.

Before you start

What to carry: the remote, a torch and a pen. Ten minutes.

Gas or electric? A mini split is all electric, a heat pump that heats and cools.

Check the remote’s model. It is printed on the remote, starting with ARC. Most Daikin wall remotes use the timer Cancel method below, and a few use a three button method.

Give it three minutes first. Daikin says the unit restarts by itself about 3 minutes after a power cut, and may stop for the same time after a big voltage swing.

Two things Daikin says before any repair. Breaker off for anything more than the remote. Daikin says to stop the unit and turn off the circuit breaker if there is a burning smell, abnormal noise, water leaking from the indoor unit or a breaker that trips often, and to call your dealer.

Do not attempt the repair yourself. Daikin’s manual warns that incorrect work can cause electric shock or fire. The checks on this page stop at things an owner can see and clear.

What the operation lamp is telling you

Daikin's own first steps depend on whether the lamp is blinking or lit, and whether the unit would not start or stopped while running.

Check 1Free, ten minutes

Do Daikin's first step for your lamp

Blinking and the unit will not start. Daikin says to turn off the power at the circuit breaker, then restart with the remote. If the lamp is still blinking, read the code and call your dealer.

It stopped while running and the lamp is blinking. Daikin asks whether anything is blocking the air inlet or outlet of the indoor or outdoor unit. Stop it, switch off the breaker, remove the obstruction and restart.

It stopped while running and the lamp is lit. Daikin says the unit may stop after a sudden large voltage swing to protect itself, and restarts in about 3 minutes.

The outdoor fan runs after you switch off. Normal. Daikin says it keeps turning for about a minute to protect the system.

Reading the code with the remote

Hold the timer Cancel button until 00 blinks, then keep pressing it. The code on the screen when the unit gives a long beep is the fault.

Check 2Free, five minutes

Find the code

Hold the timer Cancel button for 5 seconds, with the remote pointed at the indoor unit. Daikin says 00 blinks in the temperature display.

Press the timer Cancel button again and again. Each press shows the next code. A short beep means it is not that one. A long beep means the code on the screen is the fault.

00 with a long beep means no fault is stored. To leave, hold the Cancel button for 5 seconds again, or leave the remote alone for a minute.

The three button remotes. Daikin says some ARC433B remotes enter the check by pressing TEMP up, TEMP down and MODE together. The ten’s figure blinks, and you step it with TEMP until the beeps say it is right: two short beeps for the first figure, a long beep for both.

The ARC447A remote. Daikin says holding its timer Cancel button for 5 seconds takes the display straight to the code, with a long beep.

What each code means

These are the codes Daikin lists for its residential units, from its operation manual and its service list, with the likely causes from the service list.

Code	What Daikin says it means	Likely causes Daikin lists
00	Normal	No fault stored
U0	Refrigerant shortage	A shortage, or a blockage in the piping
U2	Voltage drop or main circuit overvoltage	Supply voltage, a brief power cut
U4	Indoor and outdoor units not communicating	Wiring, outdoor unit power off, a board
UA	Indoor and outdoor units do not match	Wrong model or board connected
A1	Indoor control board	The board, or electrical noise
A3	Drain level control	A clogged drain, an uphill drain, the pump
A5	High pressure control in heating, freeze-up protection in cooling	A clogged indoor filter, blocked airflow
A6	Indoor fan motor	The motor, its wiring, the board
C4	Indoor coil temperature sensor	The sensor or its plug
C9	Room air temperature sensor	The sensor or its plug
CC	Humidity sensor	The sensor or its plug
E1	Outdoor control board	The board or the wiring between units
E3	High pressure switch tripped	A dirty outdoor coil, the switch
E5	Compressor overload	A locked compressor, high pressure
E6	Compressor failed to start	The compressor, a stop valve not opened
E7	Outdoor fan motor	Something caught in the fan, the motor
E8	Compressor overcurrent	The compressor or the outdoor board
EA	Cooling and heating switching error	The four way valve, a gas shortage
F3	Discharge pipe too hot	The pipe temperature or its sensor
F6	High pressure control in cooling	Too much refrigerant, a sensor unplugged
F8	Stopped on compressor internal temperature	Technician
H0	Compressor sensor system	A loose harness, the board
H6	Compressor position detection	The compressor cable or the compressor
H8	Compressor current sensor	The inverter wiring or the board
H9	Outdoor air temperature sensor	The sensor or its plug
J3	Discharge pipe temperature sensor	The sensor or its plug
J6	Outdoor coil temperature sensor	The sensor or its plug
J8	Liquid pipe temperature sensor	The sensor or its plug
L3	Electrical parts overheating	Hot air short circuiting, the outdoor fan
L4	Inverter heatsink too hot	Hot air short circuiting, the fin sensor
L5	Output overcurrent	The compressor or the inverter board
P4	Inverter heatsink temperature sensor	The sensor or the inverter board

The checks that are yours

Check 3Free, twenty minutes

Work the owner checks, breaker off first

A5: the filters. Daikin’s first listed cause is a clogged indoor filter. Wash the filters, and make sure nothing sits in front of the unit where its air could loop straight back in: how to wash mini split filters.

U4: the outdoor unit’s power. Daikin lists the outdoor unit’s power supply being off. Check its breaker and the disconnect switch beside it.

E7: the outdoor fan. Daikin lists a fan that cannot turn because something is caught in it. With the breaker off, look for sticks, leaves or ice.

E3, L3 and L4: the outdoor unit’s air. Daikin names a dirty outdoor coil and hot air short circuiting, meaning the unit breathes its own exhaust. Clear space around it and rinse the coil: how to rinse an outdoor coil without bending the fins.

A3: the drain. Daikin lists a clogged drain and an upward slope. The drain hose must run downhill all the way: where a mini split’s water goes and how it backs up.

U2: the power. A voltage drop or a brief power cut. Switch off at the breaker, restore and restart.

When it needs a technician

Check 4

Know when to stop

U0. A refrigerant shortage means a leak somewhere, or a blockage. Sealed system work for a licensed technician: signs the refrigerant is leaking.

E6 on a new install. Daikin lists a stop valve that was never opened. That is the installer’s job to put right.

F6 after a recharge. Daikin’s first listed cause is too much refrigerant. Tell whoever last added gas.

E5, E8, H6, L5 and EA. The compressor, its drive or the four way valve. Technician work.

The sensor and board codes. C4, C9, CC, H9, J3, J6, J8, P4, A1 and E1 are a sensor, its plug or a board. Give the technician the code you read with the remote.

Questions people ask

What does U4 mean on a Daikin mini split?

The indoor and outdoor units are not communicating. Daikin lists wiring faults, the outdoor unit’s power being off, and a faulty board. Check the outdoor unit has power, then call a technician if the code returns.

What does A5 mean on a Daikin?

High pressure control in heating or freeze-up protection in cooling. Daikin’s first listed cause is a clogged indoor filter, so wash the filters first.

What does U0 mean?

A refrigerant shortage. Daikin lists a shortage or a blockage in the piping. A reset will not fix it, and it needs a technician.

How do I check the error code on a Daikin?

Point the remote at the unit and hold the timer Cancel button for 5 seconds until 00 blinks. Keep pressing it, and the code showing at the long beep is the fault.

What does 00 mean on the Daikin remote?

No fault. It is the first code the check shows, and a long beep on 00 means nothing is stored.

Why is my Daikin blinking but working again after a reset?

Daikin says lightning or radio waves can make the unit malfunction, and a restart from the breaker can clear it. If the lamp blinks again, read the code before you call.

Sources: Daikin Industries "Simple Self-Diagnosis by Malfunction Code" and "How to Check Error Codes" (SM-TS3), and Daikin's operation manual for residential wall units