Air conditioning fault codes by brand
Split air conditioning reports faults as a two-character code, and on most domestic units there is no display to show it — you have to ask the remote controller for it. Start here, because how you retrieve the code differs by manufacturer and getting it wrong can wipe it.
Brands
Pick your manufacturer to see every code we cover.
Most looked-up air conditioner codes
Across every brand in this category.
- Water dripping from the indoor unitAll brandsUsually a blocked drain rather than a failed pump. Mitsubishi say so directly: their pump runs constantly in cooling and rarely fails.Get it checked
- Not blowing coldAll brandsCheck the filter before anything else. A blocked one does not look like a dirty filter — it looks like poor cooling, icing, or a refrigerant fault.Get it checked
- How to get the fault codeAll brandsThere is no display, so you have to ask the unit. Every brand does it differently, and Toshiba's handbook says to read the code before cutting the power.Usually simple to fix
- Outdoor unit not runningAll brandsUsually not dead at all. A restart delay, a defrost or a satisfied room stops the outdoor unit by design, and on a domestic split a lit indoor unit means the supply is on.Get it checked
- U0DaikinRefrigerant shortage. The circuit is sealed, so if it is short it has leaked — and this is certified work by law, not a top-up.Get it checked
- A5DaikinFreeze-up protection or high pressure control. A filthy indoor filter is a legitimate published cause, which makes this the one on the list worth checking yourself.Get it checked
- PAMitsubishi ElectricA drain fault. Mitsubishi tell their own engineers not to assume the pump has failed — the usual cause is a blockage backing the water up.Get it checked
- U4DaikinThe indoor and outdoor units have stopped talking. Daikin’s own cause list starts with the mains supply and the inter-unit cable, so one breaker cycle is worth a try before anyone is called.Get it checked
- U1Mitsubishi ElectricU1 is a high-pressure fault on a Mitsubishi air conditioner and on an Ecodan alike. The fault is the same; the checks depend on which appliance you have.Get it checked
- E6DaikinThe compressor failed to start. It sits in Daikin’s outdoor unit group alongside the overload and pressure codes, and all of them are certified work.Get it checked
- 00DaikinNot a fault. Daikin publish 00 as NORMAL, and it is also what shows while you are stepping through the diagnostic.Usually simple to fix
- 01 - 11ToshibaAn indoor fan motor problem on the RAS domestic range. Read as a pair — initial code 01, detail code 11.Get it checked
- 2503Mitsubishi ElectricA drain sensor fault, which is the version where the tray is clean. Mitsubishi note the indoor unit may have a float switch instead of a sensor.Get it checked
- 01 - 04ToshibaIndoor to outdoor communication on the RAS range. Toshiba’s own list starts with the connecting cable and includes the outdoor unit’s protectors — and read the code before you switch anything off.Get it checked
- EFMitsubishi ElectricA non-defined error that Mitsubishi attribute to noise interference, with a published owner remedy: power down for thirty seconds.Usually simple to fix
- 03 - 1EToshibaHigh compressor discharge temperature. Toshiba group it with the locked rotor and overcurrent codes, and it points at the refrigerant circuit.Get it checked
Symptoms
No code on the display? Start from what it is doing.
Air conditioning keeps stopping
A system that runs for a while and then stops is usually protecting itself, and how long it lasts before stopping is the most useful thing you can measure.Air conditioning not cooling
Measure the difference between the air going in and the air coming out before deciding anything, because it separates a unit that is not cooling from a unit that is not cooling enough.
How air conditioning fault codes work
The first thing to know is that your air conditioner probably is not showing you a code, and that is not because there is not one.
A domestic split has an indoor unit with no screen. The fault is stored, and you retrieve it through the remote controller or by reading a flashing light. Every manufacturer does this differently and the differences matter. On Daikin you hold Cancel for five seconds and press it repeatedly until you get a long continuous beep, which means the code shown is yours — a short beep or two beeps means you are passing over codes that do not apply. On Toshiba's domestic range you press CHK to enter a service mode and step through with the timer buttons. On Fujitsu the same fault has as many as four different published forms depending on whether you are reading the remote, counting lamp flashes, looking at the app or at the wireless indicator, so two people with the same fault can be searching completely different strings.
One instruction is worth reading before you touch anything, because it is the opposite of what everyone does. Toshiba state plainly that you should not turn the power off before reading the fault codes, because doing so clears the diagnostic memory. The universal instinct on a misbehaving appliance is to switch it off and on, and on a Toshiba that destroys the only evidence of what went wrong. Get the code first.
Now the part that decides who fixes it. An air conditioner is a sealed refrigerant circuit joined to a substantial electrical supply, and the refrigerant side is legally restricted work — handling fluorinated gas requires certification, and that covers pressures, charge, leak detection, recovery, the compressor, the expansion valve and the four-way valve. A large share of the published codes point straight at that circuit. What is genuinely yours is narrow but real: the indoor filter, the condensate drain, the space around the outdoor unit, the isolator, and the remote's batteries. The indoor filter is worth more attention than it gets, because a blocked one does not present as a dirty filter. It presents as freezing up, as poor cooling, and on some systems as a code that reads like a refrigerant fault — Mitsubishi name a blocked indoor coil as a cause of a low-pressure sensor reading.
Water dripping from an indoor unit is the commonest complaint in the category and it has a published answer that is not what people assume. Mitsubishi are unusually direct about it: do not assume the drain pump is faulty, because on their equipment the pump runs whenever the unit is cooling, it is robust, and it does not often fail. The usual cause is a blocked drain pipe or drip tray backing the water up. That is worth knowing before somebody quotes you for a pump.
Two published traps to finish with, both of which make a working machine look broken. Daikin publish a code of 00, and 00 means normal. Mitsubishi publish a code whose stated cause is, in their own word, "Normal" — and another that means somebody left a test-operation switch on. And on Toshiba's RAV range the first number on the display is not a fault code at all: it is a count of compressor starts, printed in hexadecimal.