Daikin Mini Split Error Codes: U4, U2, E5 and What Each Means

Daikin mini-split and heat pump systems show a two-character error code on the indoor unit’s display, or signal it by blinking the operation and timer LEDs, when a fault is detected. The first character is a letter that points to the affected area — A and C codes relate to the indoor unit and its sensors, E codes to the outdoor unit and compressor, F, H, L and P codes to the refrigerant system and compressor, and U codes to system-level problems such as communication, power supply, or low refrigerant. The second character narrows down the specific fault. Use the quick-answer table above to find your exact Daikin error code, what it means, and the safe first step. Some codes clear after a simple power cycle; others — especially compressor, refrigerant, and sensor faults — require a licensed technician. Always confirm the meaning against the code list in your model’s Daikin manual, as codes can vary slightly by unit.

How to read a Daikin error code

Where the code appears depends on your unit type:

• Wall-mounted units: the code shows on the indoor unit’s display, or the unit flashes the operation and timer LEDs in a pattern. Pressing the Cancel/Timer button on the remote often prompts the unit to display the stored code.
• Ducted and concealed units: the code is usually reported through the wired controller (thermostat).

What the first letter tells you

What to do first

For non-safety codes (communication, fan, airflow, sensor reads), a single power cycle resolves many transient faults:

1. Turn the unit off with the remote.
2. Switch off the circuit breaker feeding the system for about one minute.
3. Restore power and let the unit restart.

If the same code returns, stop — a repeating code means the underlying problem is still present and needs diagnosis. Do not keep resetting compressor or refrigerant codes.

The codes people look up most, step by step

Daikin U4

A Daikin mini split constantly sends data between the indoor and outdoor PCBs over the interconnecting cable. On Daikin’s residential range those terminals are numbered No. 1, No. 2 and No. 3, with wire No. 3 carrying the signal; on VRV and SkyAir the transmission pair is F1 / F2. (Daikin does not use S1/S2/S3 — that is Mitsubishi’s labelling.) When the outdoor unit doesn’t respond, the system flags U4 and usually stops heating or cooling.

UF is not the same fault. Daikin’s malfunction code list defines UF as system is not set yet — the commissioning check operation was never run, or a stop valve is still closed. It shows up during installation for that reason, not because of a communication failure.

Full detail, including what the U4-01 and U4-03 suffixes mean and Daikin’s own diagnostic flow chart, is on our Daikin U4 error code page.

Common causes

• Loose or corroded wiring connections at the indoor or outdoor terminal block.
• Miswiring (very common on new installs) — reversed or wrong-terminal connections.
• No power to the outdoor unit — a tripped breaker or an off disconnect switch.
• Damaged signal cable — pinched, rodent-chewed, or weather-degraded.
• Faulty indoor or outdoor control board (PCB).

How to fix it

1. Power-cycle once: turn the unit off, switch its breaker off for ~1 minute, then restore power.
2. Confirm outdoor power: make sure the breaker and the outdoor disconnect are on — a dead outdoor unit looks like a communication loss. See our guide to an outdoor unit not running if it stays off.
3. If U4 returns, stop resetting and have a technician inspect the interconnecting wiring — terminals No. 1 to No. 3 on a residential system, F1/F2 on VRV — and the control boards. Our Daikin U4 error code page walks Daikin’s own flow chart step by step.

Daikin E5

E5 is a compressor overload / overheat protection. When the outdoor unit can’t reject heat efficiently — or the compressor is straining — current and temperature climb, and the control board shuts the compressor down to protect it. Clearing the underlying heat or load problem is what resolves it.

Common causes

• Blocked outdoor airflow — leaves, dirt, or a dirty condenser coil trapping heat.
• Dirty indoor filter — restricts airflow and raises system load.
• High outdoor temperatures — extreme heat pushes the compressor near its limit.
• Refrigerant charge problem — over- or undercharge (a leak) raises pressure/heat.
• Electrical — a weak run capacitor making the compressor strain to start.
• Failing compressor — internal wear; E5 returns no matter what.

How to fix it

1. Turn it off and let it cool — give the compressor time before doing anything.
2. Restore airflow: clear debris around the outdoor unit, clean the outdoor coil, and wash the indoor filter.
3. Power-cycle once at the breaker. If cooling is weak, see why a mini split isn’t cooling.
4. If E5 returns, stop resetting and call a technician — it’s a sealed-system or compressor fault.

Daikin U2

A Daikin inverter system needs stable voltage within a set range. When the supply drifts outside that window — or sags under load — the board reports U2 and stops the compressor to avoid damage. Restoring clean, stable voltage is what clears it.

Common causes

• Tripped breaker or an unstable connection at the panel.
• Low or high line voltage from the utility or household wiring.
• Voltage drop from loose terminals or undersized power wiring.
• Overloaded / shared circuit — the unit should be on its own dedicated circuit.
• Brownout or utility event.
• Power-circuit or main PCB fault inside the unit.

How to fix it

1. Check the breaker and reset it once if tripped.
2. Power-cycle once — off at the breaker for ~1 minute, then back on. If the unit won’t start at all afterward, see mini split not turning on.
3. Look for supply clues — dimming lights or other misbehaving appliances point to a household/utility voltage problem.
4. If U2 returns, have an electrician or HVAC technician measure the voltage and inspect the power wiring.

Daikin H6

To run a modern inverter compressor smoothly, the outdoor PCB must read the compressor’s rotor position. If that signal is missing or implausible, the board reports H6 and won’t energize the compressor. The fix is restoring that signal — which almost always involves the wiring, the inverter board, or the compressor.

Common causes

• Compressor wiring fault — loose, corroded, or incorrect U/V/W connections.
• Outdoor fan or coil blocked — the compressor starting against a stalled, overheated condition.
• Inverter PCB fault — the board can’t read or process the position signal.
• Failing compressor — internal fault preventing a valid position reading.

How to fix it

1. Power-cycle once — off at the breaker for ~1 minute, then back on.
2. Clear the outdoor unit — make sure the fan spins freely and the coil is clear. If the outdoor unit still won’t run, see outdoor unit not running.
3. If H6 returns, stop and call a technician to test the compressor wiring, inverter board, and compressor.

Trademark note: “Daikin” is a trademark of Daikin Industries, Ltd. This page is an independent homeowner resource and is not affiliated with, authorized by, or endorsed by Daikin. Brand and code references are used factually for identification and troubleshooting only.