Daikin error codes follow a clear logic. The letter tells you the area of the system: A for the indoor unit, C for indoor sensors, E, F, H, J, L and P for the outdoor unit, and U for system-wide problems such as communication or refrigerant. The number narrows it down.
The meanings below come from Daikin’s Simple Self-Diagnosis by Malfunction Code chart (SM-TS3), which covers room air conditioners, Sky Air and VRV systems. Not every code applies to every model, so use it alongside your own manual. We repair Daikin systems across London and the South East as part of our /air-conditioning-repair/ service.
How to see the code
On systems with a wired controller, the code appears on the controller screen. Wall units with a handheld remote report faults in a way that varies by model, so check your operation manual for how yours shows a code. If you can’t read it, note what the indicator lamps are doing and the model number from the label on the indoor unit. That’s enough for an engineer to start.
Indoor unit codes (A and C)
| Code | Meaning (Daikin) | Likely causes listed by Daikin |
|---|---|---|
| A1 | Indoor unit PCB malfunction | Faulty indoor board; external electrical noise |
| A3 | Drain level control abnormality | Clogged or badly sloped drain line, faulty drain pump or float switch |
| A5 | High-pressure control (heating) or icing protection (cooling) | Clogged air filter, short circuit of air, faulty indoor coil thermistor |
| A6 | Fan motor malfunction | Damaged harness or loose connector, faulty fan motor or indoor board |
| C4 | Liquid pipe (heat exchanger) thermistor malfunction | Faulty thermistor or board, poor connector contact |
| C7 | Front panel drive motor fault | Faulty front panel motor or limit switch |
| C9 | Suction air thermistor malfunction | Faulty thermistor or board, poor connector contact |
Source: Daikin SM-TS3 chart. A3 and A5 are the two indoor codes most often linked to things you can see: a blocked drain or a dirty filter.
Outdoor unit codes (E, F, H, J, L, P)
| Code | Meaning (Daikin) |
|---|---|
| E1 | Outdoor unit PCB defect |
| E5 | Inverter compressor motor lock or overheat |
| E6 | Compressor overcurrent or lock |
| E7 | Outdoor fan motor system malfunction (debris blocking the fan is one listed cause) |
| E8 | Inverter compressor overcurrent |
| F3 | Discharge pipe temperature abnormality |
| F6 | Abnormal high pressure or refrigerant overcharge |
| H0 | Compressor sensor system malfunction |
| H6 | Compressor position detection sensor malfunction |
| H8 | Compressor input (CT) system malfunction |
| H9 | Outdoor air thermistor malfunction |
| J3 | Discharge pipe thermistor malfunction |
| J6 | Outdoor heat exchanger thermistor malfunction |
| L3 | Electrical component box overheating |
| L4 | Inverter heat sink (fin) overheating |
| L5 | Inverter instantaneous overcurrent (DC output) |
| P4 | Radiation fin temperature sensor malfunction |
Source: Daikin SM-TS3 chart. These are engineer codes. Most involve the inverter board, compressor or outdoor sensors.
Want it done properly? AirCon Doctor installs, repairs and services air conditioning and heat pumps across London and the South East, from our base in East Grinstead. We’re an F-Gas certified company and NICEIC approved. Get a fixed-price quote.
System codes (U)
| Code | Meaning (Daikin) | Likely causes listed by Daikin |
|---|---|---|
| U0 | Refrigerant shortage | Low refrigerant or a restriction in the pipework, faulty sensor or board |
| U2 | Power supply abnormality or momentary power failure | Abnormal supply voltage, a brief power cut, wiring fault |
| U4 | Transmission error between indoor and outdoor units | Wiring fault on the transmission line, outdoor unit switched off, faulty board |
| UA | Indoor/outdoor combination error | Mismatched units or settings, or a power supply defect |
U0 is the one to take seriously. A refrigerant shortage means a leak somewhere, and a sealed system shouldn’t lose refrigerant. See /air-conditioning-regas-guide/ for why a top-up alone isn’t a fix.
What you can safely check yourself
- Filters (A5). A clogged filter is the first cause Daikin lists for A5. Clean them and let any ice melt before restarting.
- Drain (A3). Check the drain hose outlet outside isn’t blocked, kinked or buried. Don’t take the unit apart.
- Outdoor unit (E7). Look for leaves, snow or debris around the fan. Clear it from the outside only, with the power off.
- Power (U2, U4). Check the isolator next to the outdoor unit is on, and the breaker hasn’t tripped. A brief power cut can cause U2.
- One restart. Power off at the isolator for a few minutes, then restart. If the code returns, leave it off.
Our /ice-on-air-conditioning-unit/ guide covers icing in more detail.
When to call an F-Gas engineer
Call an engineer if a code comes back after one restart, for any E, F, H, J, L or P code, for U0 at any time, and for UA after any work on the system. Refrigerant work, including leak finding and recharging, must be done by an F-gas certified company with qualified engineers (GOV.UK company certification). Systems with 5 tonnes CO2 equivalent or more of refrigerant also need regular leak checks by law.
We’re F-Gas certified and NICEIC approved. A repair call-out with diagnosis starts from £75 + VAT, followed by a fixed price for the repair. We’re independent engineers rather than a Daikin-accredited installer, and we repair and service Daikin systems of all ages. See /daikin-air-conditioning/.
Daikin warranty before you book a repair
Daikin’s standard warranty on split air conditioning is 2 years; its 5 to 7 year extensions apply to air-to-water (Altherma) units only (Daikin warranty). If your split system is within 2 years of installation, contact your installer first and keep your commissioning and service records ready. Our /air-conditioning-warranty-guide/ explains how warranty claims usually work.
Quick answers
What does A3 mean on a Daikin air conditioner?
Daikin lists A3 as a drain level control abnormality. The usual causes are a clogged or badly sloped drain line, a failed drain pump or a faulty float switch.
What does U4 mean on Daikin?
U4 is a transmission error between the indoor and outdoor units. Check the outdoor isolator is on and try one restart. If it returns, an engineer needs to check the wiring and boards.
What does A5 mean on a Daikin?
A5 is high-pressure control in heating or icing protection in cooling. Daikin lists a clogged air filter as the first likely cause, so clean the filters before anything else.
What does U0 mean on Daikin air conditioning?
U0 means refrigerant shortage. The system has probably leaked. An F-gas certified engineer needs to find and repair the leak before recharging.
Related services
- Air conditioning repair
- Daikin air conditioning
- Air conditioning regas
- Emergency air conditioning repair
More advice
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- Why Is My Air Conditioning Leaking Water? Causes and Fixes
- Ice on Your Air Conditioning Unit: What It Means and What to Do
- All advice
This guide is general information, checked against the sources linked on 30 October 2026. It isn’t legal, tax or financial advice. Rules, grants and product ranges change, so check the current position before you rely on it.