Daikin fault codes are two characters: a letter that identifies the subsystem and a digit that identifies the specific fault. A-codes are indoor unit faults, C-codes are sensors, E and F cover the outdoor unit and its pressures, H and J are compressor and sensor systems, L is the inverter, and U-codes are system, wiring and refrigerant faults. Most Daikin codes need a technician — the exceptions are the ones caused by dirty filters and blocked airflow.
Reading the code from the remote
On many Daikin wall-mounted splits the fault code is not shown until you ask for it. Point the remote at the indoor unit and hold the Cancel button (the timer cancel button on some remotes) for about five seconds. The display enters diagnosis mode and starts stepping through characters; press the button repeatedly and the unit answers with a short beep for each wrong character and a long beep when it reaches the stored code. Do the same for the second character. Units with a wired controller or a ducted system display the code directly instead.
If the unit has been powered off since the fault occurred, the code may have cleared. Note it down before you reset anything.
What the letter groups mean
Daikin uses the same code structure across splits, ducted systems and VRV, so the first character narrows the problem down immediately:
- A — indoor unit: control board, protection devices, fan motor.
- C — sensor system: indoor thermistors reading out of range.
- E — outdoor unit: control board, high pressure, compressor protection.
- F — discharge pipe and pressure faults.
- H — compressor, position detection and related sensors.
- J — outdoor sensor systems.
- L — inverter faults.
- U — system-level faults: refrigerant shortage, wiring, power supply, unit combination.
Common Daikin error codes
| Code | Meaning | Typical cause |
|---|---|---|
| A1 | Indoor unit PCB fault | Failed indoor control board |
| A5 | Freeze-up protection in cooling, high pressure control in heating | Clogged indoor filter or a faulty indoor coil thermistor |
| A6 | Indoor fan motor fault | Locked or overloaded fan motor, or a bad connection |
| C4 | Indoor heat exchanger thermistor resistance abnormal | Disconnected or short-circuited sensor |
| C9 | Indoor suction air thermistor resistance abnormal | Disconnected or short-circuited sensor |
| E5 | Compressor overload / overheat protection | Restricted refrigerant flow or low charge |
| E7 | Outdoor fan motor fault | Failed DC fan motor or fan motor driver |
| F3 | Discharge pipe temperature too high | Low refrigerant, restriction, or a faulty discharge sensor |
| H6 | Compressor position detection sensor fault | Inverter has lost rotor position feedback |
| U0 | Refrigerant shortage | Leak, closed stop valve, or a blocked pipe |
| U2 | Power supply fault | Voltage out of range or an inverter supply problem |
| U4 | Indoor / outdoor communication error | Interconnecting wiring error or a control board |
| UA | Indoor and outdoor unit combination error | Wrong models or quantity paired, or a site setting error |
What you can check yourself
Filters, room airflow and the space around the outdoor unit are yours. Control boards, stop valves, refrigerant lines and anything behind an electrical cover are not — Daikin outdoor units contain inverter capacitors that stay charged after the power is off.
- Clean or replace the indoor filters
A5 in cooling means the indoor coil is icing up, and the most common reason is that the coil is not getting enough air across it. Wash the mesh filters, let them dry, and refit. If the coil is already frozen, run the unit in fan-only mode for an hour to thaw it before restarting cooling.
- Free up the airflow path
Check the indoor unit is not blowing into a curtain or a piece of furniture, and that the return path is clear. On a ducted system, open any closed registers — closing too many rooms off starves the coil in exactly the same way a dirty filter does. Our guide on an air conditioner freezing up covers this in more detail.
- Clear the outdoor unit
Pull weeds, leaves and debris away from the outdoor unit and make sure it has clear space on all sides. Restricted condenser airflow raises discharge pressures and temperatures, which is the mechanism behind E5 and F3.
- Check the power supply for U2
Look at the breaker feeding the outdoor unit and at the outdoor isolator. If a breaker has tripped, reset it once. If it trips again, or the house has been having voltage problems, stop and get an electrician — an inverter running on out-of-spec voltage is being damaged, not merely inconvenienced.
- Reset once, then observe
Switch the system off at the breaker for two minutes and restart. Note whether the code returns, how long the unit ran first, and whether it was heating or cooling. Codes that reappear immediately, and every U0 or H6, mean the fault is still present.
U0 reports a refrigerant shortage. Split systems do not consume refrigerant, so a shortage means it escaped. Topping the system up without finding the leak is a temporary fix that also breaks refrigerant handling rules in most countries — refrigerant work requires a certified technician. Running a system on a low charge overheats the compressor, which is why U0 and E5 often show up together.
When to call a professional
Every code in the A1, E, F, H, J, L and U groups needs a Daikin-competent technician, as do C-codes once you have ruled out an obvious airflow cause. Call promptly for U0, E5, F3 and H6 — all four involve the compressor running outside its safe envelope, and the cost of the eventual repair rises the longer the system is left running. UA usually appears after an install or a part swap and means the paired units or a site setting are wrong; the installer should correct it.
