Fujitsu air conditioners display error codes through two methods: alphanumeric codes on the remote control or wired controller, and LED flash patterns on the outdoor unit. The flash patterns are particularly useful when the indoor unit cannot communicate with the outdoor unit, as the outdoor LED will still indicate the fault.
This guide covers every Fujitsu error code for their UK residential and commercial range, including wall-mounted splits, multi-splits, ducted systems, and the Airstage VRF range. We have included both the standard error code table and the outdoor unit flash pattern guide.
How to Read Fujitsu Error Codes
Remote Control / Wired Controller Display
Error codes appear as a two-character alphanumeric code on the remote control screen or wired controller. Codes starting with "O" (the letter, not zero) indicate communication and sensor faults. Codes starting with numbers indicate system-level faults.
Outdoor Unit LED Flash Patterns
The green operation LED on the outdoor unit flashes in a repeating pattern. Count the number of flashes between pauses to identify the code. Some patterns use timed on/off sequences rather than flash counts (detailed in the flash pattern table below).
For the complete technical documentation for your specific model, check the Fujitsu General UK downloads page.
Standard Fujitsu Error Codes
| Code | Meaning | What It Means and What to Do |
|---|---|---|
| OO | Indoor to remote communication failure | The remote controller cannot communicate with the indoor unit. Check for obstructions between the remote and the receiver, replace the remote batteries, and make sure the receiver window on the indoor unit is clean. |
| O1 | Indoor to outdoor communication failure | The indoor and outdoor units cannot talk to each other. Check the interconnecting cable for loose connections, damage, or incorrect wiring. This is one of the most common Fujitsu error codes. |
| O2 | Indoor air temperature sensor open circuit | The room temperature sensor has an open circuit (disconnected or wire broken). Check the sensor connector on the indoor PCB. Sensor replacement is needed if the wiring is intact. |
| O3 | Indoor air temperature sensor short circuit | The room sensor has a short circuit. Same checks as O2. The sensor has failed and needs replacement. |
| O4 | Indoor pipe temperature sensor open circuit | The indoor coil temperature sensor is disconnected or has a broken wire. |
| O5 | Indoor pipe temperature sensor short circuit | The indoor coil sensor has a short circuit and needs replacement. |
| O6 | Outdoor pipe temperature sensor fault | The outdoor coil temperature sensor has failed. Located on the outdoor unit, needs an engineer to access. |
| O8 | Power source connection failure | The power supply to the unit is incorrect or unstable. Check the breaker, wiring, and supply voltage. |
| O9 | Drain problem - float switch operated | The condensate drain pan is full. The float switch has triggered to prevent overflow. Clear the drain line with a vacuum or compressed air, and clean the drain pan. |
| OA | Outdoor air temperature sensor fault | The outdoor ambient temperature sensor has failed. |
| OC | Discharge temperature sensor fault | The compressor discharge pipe temperature sensor has failed. |
| OE | High pressure heatsink error | The outdoor unit's high pressure protection or heatsink temperature protection has activated. |
| 11 | Outdoor PCB fault | The outdoor unit's main circuit board has failed. Requires board replacement by a qualified engineer. |
| 12 | Indoor fan motor fault | The indoor fan motor is not running or running at the wrong speed. Check for physical obstructions first. If clear, the motor or its driver circuit has failed. |
| 13 | Outdoor signal abnormal / indoor signal error | Data signal errors between indoor and outdoor units. Check interconnecting wiring. |
| 14 | Outdoor EEPROM fault | The outdoor unit's memory chip has failed. Board replacement or reprogramming needed. |
| 15 | Compressor temperature failure | The compressor temperature sensor or the compressor itself is overheating. Needs professional diagnosis. |
| 16 | Pressure switch error | The high or low pressure switch has triggered. This indicates a refrigerant system fault and needs an F-Gas certified engineer. |
| 17 | IPM (Intelligent Power Module) error | The inverter power module has failed. This is a serious fault requiring board replacement. |
| 18 | CT (Current Transformer) error | The compressor current monitoring circuit has detected an anomaly. Could indicate a failing compressor or electrical fault. |
| 19 | Active filter module error | The active noise filter module has failed. |
| 1A | Compressor failure | The compressor has failed to start or has seized. This is a major fault requiring compressor replacement. |
| 1B | Outdoor fan motor failure | The outdoor fan is not running. Check for obstructions, then check the motor and its connections. |
| 1C | Inverter to PCB communication failure | The inverter board cannot communicate with the main outdoor PCB. |
| 1D | Two-way valve sensor fault | The sensor on the two-way (liquid) valve has failed. |
| 1E | Expansion valve error | The electronic expansion valve is not operating correctly. Valve motor or coil failure. |
| 1F | Indoor unit connection error | An indoor unit in a multi-split system is not properly connected or configured. |
| 20 | Indoor manual switch abnormal | The manual override switch on the indoor unit is stuck or faulty. |
| 24 | High pressure protection (cooling mode) | Excessive high pressure detected during cooling operation. Check for blocked condenser, restricted airflow, or refrigerant overcharge. |
| 25 | PFC circuit error | The power factor correction circuit has failed. |
| 26 | Indoor signal error | Signal processing error on the indoor PCB. |
| 27 | Indoor signal error (alternate) | Secondary signal processing error on the indoor PCB. |
| 28 | Indoor heat exchanger temperature error | The indoor coil temperature is reading outside normal parameters. |
| 29 | Outdoor heat exchanger temperature error | The outdoor coil mid-point temperature sensor is reading abnormally. |
| 2A | Power supply frequency detection error | The unit cannot detect the correct power supply frequency (50Hz in the UK). |
| 2B | Compressor temperature error | Compressor temperature is outside safe limits. |
| 2C | Four-way valve abnormal | The reversing valve is not switching properly between heating and cooling modes. |
Outdoor Unit LED Flash Patterns
When the outdoor unit's green LED flashes in a pattern, count the flashes to identify the fault:
| Flash Pattern | Meaning |
|---|---|
| 1 flash | Communication error between indoor and outdoor units |
| 2 flashes | Discharge pipe temperature sensor fault |
| 3 flashes | Outdoor heat exchanger outlet temperature sensor fault |
| 4 flashes | Outdoor ambient temperature sensor error |
| 5 flashes | Outdoor heat exchanger mid-point temperature sensor fault |
| 6 flashes | Discharge pipe temperature abnormally high |
| 7 flashes | Compressor temperature sensor fault |
| 8 flashes | Heatsink temperature sensor fault |
| 9 flashes | Pressure switch abnormal |
| 10 flashes | Compressor temperature abnormally high |
| 12 flashes | IPM (power module) error |
| 13 flashes | Compressor rotor position cannot be detected |
| 14 flashes | Compressor cannot start |
| 15 flashes | Outdoor fan abnormal (upper fan) |
| 16 flashes | Outdoor fan abnormal (lower fan) |
Timed Flash Patterns
Some faults use timed on/off sequences rather than flash counts:
| Pattern | Meaning |
|---|---|
| 5 sec on / 0.1 sec off (repeating) | PAM voltage abnormality |
| 5 sec on / 1 sec off (repeating) | Protection operation active |
| 5 sec on / 2 sec off (repeating) | PFC surge protection (permanent stop) |
| 5 sec on / 5 sec off (repeating) | Fan malfunction |
| 2 sec on / 2 sec off (repeating) | CT (current transformer) abnormality |
| 2 sec on / 5 sec off (repeating) | Compressor temperature protection (permanent stop) |
| 1 sec on / 1 sec off (repeating) | Pump down operation (not a fault) |
| 0.5 sec on / 0.5 sec off (repeating) | Current surge protection |
| 0.1 sec on / 0.1 sec off (repeating) | Thermistor malfunction |
| 0.1 sec on / 2 sec off (repeating) | Compressor position detection malfunction |
| Steady off | Normal operation or power disconnected |
Troubleshooting: What You Can Check Yourself
- Code OO (remote comms failure) - Replace the remote control batteries. Clean the infrared receiver window on the indoor unit. Try pointing the remote from directly in front of the unit at close range.
- Code O9 (drain problem) - This is the most DIY-friendly Fujitsu error. Clear the condensate drain line using a wet vacuum at the outdoor drain outlet. Clean the drain pan inside the indoor unit. If the drain pump is fitted, check it is running.
- Code O1 (indoor/outdoor comms) - Check the interconnecting cable between units. Look for loose terminals at both ends. If the cable runs through walls, check for damage from rodents or building work.
- Sensor faults (O2-O6, OA, OC) - If you are comfortable opening the unit, check the sensor connectors are firmly seated on the PCB. Corroded or loose connectors cause intermittent sensor faults.
- Power reset - For any error, try switching off at the isolator for 60 seconds. This clears temporary faults from power surges or sensor glitches.
When to Call a Professional
- Pressure switch and compressor codes (16, 1A, 15, 24) - These involve the sealed refrigerant system or high-voltage compressor components. Only F-Gas certified engineers should handle these.
- IPM and inverter codes (17, 1C, 25) - Power electronics faults carry serious electrical risk.
- Timed flash patterns showing "permanent stop" - The outdoor unit has detected a condition serious enough to prevent automatic restart. It needs professional diagnosis before it can safely run again.
- Any code that returns after a power cycle - Persistent faults indicate a genuine hardware issue, not a temporary glitch.
UK Regulations for Fujitsu AC Systems
- F-Gas Regulation - Fujitsu systems using R32 or R410A require regular leak checks by F-Gas certified engineers. See the UK Government F-Gas guidance.
- TM44 Inspections - Systems over 12kW combined cooling capacity must be inspected every five years. See UK Government air conditioning inspections.
Official Fujitsu Resources
- Fujitsu General UK - Official UK product pages and support contacts.
- Fujitsu UK Downloads - Installation manuals, technical datasheets, and service documentation for all UK models.
- Fujitsu UK Support - Technical support contact details and service enquiries.
Written by
Ali Elm
Ali is the Head of Operations at Be Cool Refrigeration with over a decade of hands-on experience in HVAC and commercial refrigeration. He oversees every installation, repair, and maintenance project, making sure the work meets the highest standards. Ali holds full F-Gas certification and has worked across residential, commercial, and industrial refrigeration systems throughout London and the South East. When he is not on site, he writes these guides to help business owners and homeowners understand their cooling systems better.