Hitachi air conditioning alarm codes are two characters, mostly two digits such as 02, 03 or 08, plus b0, b1 and EE. On systems with a wired controller, the code appears with the number of the indoor unit that raised it. 03 is a communication fault between the indoor and outdoor units, 02 is the outdoor unit's high pressure cut, 08 is high discharge gas temperature and 31 is an incorrect capacity setting between the units.
If you have seen Hitachi lists with codes such as E01, F01 or P01, treat them with caution. We could not find that format in any Hitachi document, and Hitachi says its alarm code "language" is used across its product ranges. Every code on this page comes from Hitachi's own published manuals.
At a glance
| Question | Answer |
|---|---|
| Indoor and outdoor units not communicating | 03, or 04 for the inverter PCB and outdoor PCB |
| Pressure or temperature protection | 02 (high pressure cut), 07, 08, and 41 to 47 |
| Sensor or thermistor failure | 11 to 14 (indoor unit), 20 to 24 and 29 (outdoor unit) |
| Fan problem | 19 (indoor fan), 09 and 56 to 58 (outdoor fan) |
| Power supply | 05 (power source phases) or 06 (voltage drop in the outdoor unit) |
| Installation or setting problem | 31, 32, 35, 36, b0 or b1 |
| Where the code shows | On the indoor unit's control screen, with the outdoor unit's code on a panel behind a detachable door |
Source: Hitachi operation manual P5417020 for RPI and RPIM FSN3 indoor units, and Hitachi Cooling & Heating.
How Hitachi shows an alarm code
According to Hitachi Cooling & Heating, "Indoor units display them on their control screen and outdoor units display their error codes on the panel which is located behind a detachable door." Hitachi also says its error code "language" is used on all of its products within each range, and that the majority of the codes are the same across regions.
On a wired controller, Hitachi's operation manual explains that the red RUN indicator flashes and the display shows the indoor unit number, the alarm code and the unit code. Write all of them down before you do anything else, because the engineer needs the unit number as much as the code on a multi-unit system.
Hitachi's residential wall-mounted units have their own fault indications, described in each model's operation manual. For a single wall unit with no wired controller, that manual is the place to check how your model shows a fault.
Hitachi alarm code list
These are the alarm codes from Hitachi's operation manual for RPI and RPIM FSN3 indoor units, an inverter-driven multi-split and VRF range, written as Hitachi writes them. Each meaning starts with the part of the system the code relates to.
Hitachi alarm codes (VRF and multi-split systems with a wired controller)
| Code | What Hitachi says it means |
|---|---|
| 01 | Indoor Unit: Activation of Protection Device |
| 02 | Outdoor Unit: Activation of Protection Device (High Pressure Cut) |
| 03 | Communication: Operational Irregularities between Indoor and Outdoor |
| 04 | Communication: Problem between Inverter PCB and Outdoor PCB |
| 05 | Supply Phase: Problem of Power Source Phases |
| 06 | Voltage: Abnormal Voltage Drop in Outdoor Unit |
| 07 | Cycle: Decrease in Superheated Discharge Gas |
| 08 | Cycle: Increase in Discharge Gas Temperature |
| 09 | Outdoor Unit: Activation of Protection Device for Outdoor Fan |
| 11 | Sensor on Indoor Unit: Inlet Air Thermistor Failure |
| 12 | Sensor on Indoor Unit: Outlet Air Thermistor Failure |
| 13 | Sensor on Indoor Unit: Freeze Protection Thermistor Failure |
| 14 | Sensor on Indoor Unit: Gas Piping Thermistor Failure |
| 19 | Fan Motor: Activation of Protection Device for Indoor Fan |
| 20 | Sensor on Outdoor Unit: Compressor Thermistor Failure |
| 21 | Sensor on Outdoor Unit: High Pressure Sensor Failure |
| 22 | Sensor on Outdoor Unit: Outdoor Air Thermistor Failure |
| 23 | Sensor on Outdoor Unit: Discharge Gas Thermistor Failure |
| 24 | Sensor on Outdoor Unit: Evaporating Thermistor Failure |
| 29 | Sensor on Outdoor Unit: Low Pressure Sensor Failure |
| 31 | System: Incorrect Capacity Setting of Outdoor Unit and Indoor Unit |
| 32 | System: Incorrect Setting of Other Indoor Unit Number |
| 35 | System: Incorrect Setting of Indoor Unit No. |
| 36 | System: Incorrect Indoor Unit Combination |
| 38 | System: Problem with Protective Pickup Circuit in Outdoor Unit |
| 39 | Compressor: Problem with Running Current at Constant Speed Compressor |
| 41 | Pressure: Overload Cooling |
| 42 | Pressure: Overload Heating |
| 43 | Protection Device: Activation of Pressure Ratio Decrease Protection Device |
| 44 | Protection Device: Activation of Low Pressure Decrease Protection Device |
| 45 | Protection Device: Activation of Low Pressure Increase Protection Device |
| 46 | Protection Device: Activation of High Pressure Increase Protection Device |
| 47 | Protection Device: Activation of High Pressure Decrease Protection Device |
| 48 | Protection Device: Activation of Overcurrent Protection Device |
| 51 | Inverter: Problem with Inverter Current Sensor |
| 52 | Inverter: Activation of Inverter Overcurrent Protection |
| 53 | Inverter: Activation of Transistor Module Protection |
| 54 | Inverter: Abnormality of Inverter Fin Temperature |
| 56 | Outdoor Fan: Abnormality of Detection for Fan Motor Position |
| 57 | Outdoor Fan: Activation of Fan Controller Protection |
| 58 | Outdoor Fan: Abnormality of Fan Controller |
| b0 | System: Incorrect Setting of Unit Capacity |
| b1 | System: Incorrect Setting of Unit and Refrigerant Cycle No. |
| EE | Compressor: Compressor Protection Alarm |
What the code groups mean
- 01 to 09: protection devices, communication and power. A protection device has stopped the indoor or outdoor unit, the units have lost communication, or there is a problem with the power supply phases or voltage.
- 11 to 29: sensors. A thermistor or pressure sensor in the indoor or outdoor unit has failed, so the system can no longer read a temperature or pressure it relies on.
- 31 to 38: system settings. These usually appear on new installations or after a part is changed: capacity, unit numbers or unit combinations that do not match.
- 39 to 48: compressor, pressure and protection. The system has detected overload, abnormal pressures or overcurrent, and has stopped to protect the compressor.
- 51 to 58: inverter and outdoor fan. Faults in the inverter's current sensing, transistor module or fin temperature, or in the outdoor fan motor and its controller.
- b0, b1 and EE. Unit capacity and refrigerant cycle setting errors, and the compressor protection alarm.
What you can check yourself
Hitachi's operation manual lists a few checks an owner can safely make before calling anyone:
- Power. Check that the main power source is on, and that the fuse has not blown or the circuit breaker tripped.
- Outdoor unit airflow. When the unit shuts down soon after starting in cooling, check that the outdoor unit's air inlet and outlet are not covered with paper, plastic or other objects.
- Filters and settings. If cooling or heating is weak, check the operation mode and set temperature, and that the air filter is not clogged.
Where the alarm stays, Hitachi's instruction is to check the details on the controller and contact your installer or distributor, giving the unit model, a description of the problem and the alarm code.
Safety
Hitachi's manual is clear on three points. If there is a burning smell or anything similar, stop the unit and turn off the main power immediately. Do not tamper with or attempt to repair electrical wiring or connections. And the piping inside the unit is charged with refrigerant under high pressure, so refrigerant work is for qualified engineers only, which in the UK means the F gas qualifications set out by GOV.UK.
When to call an engineer
- Any pressure, compressor or inverter code: 02, 07, 08, 39 to 48, 51 to 54 and EE.
- Any sensor failure code, because the unit cannot control itself properly without that reading.
- Communication or setting codes that appear after installation work, which usually need the installer back to correct wiring or settings.
- Any code that returns after you have checked the power, the filters and the outdoor unit's airflow.
Our guide to air conditioning refrigerants explains why pressure-related faults so often lead back to the refrigerant charge.
Questions people ask about Hitachi error codes
What do Hitachi air conditioner error codes mean?
They are two-character alarm codes that identify which part of the system has stopped it, such as 03 for a communication fault between the indoor and outdoor units or 08 for an increase in discharge gas temperature. Hitachi says the same code language is used across its product ranges.
Where do I find the error code on a Hitachi air conditioner?
On systems with a wired controller, the code shows on the controller screen with the indoor unit number while the red RUN indicator flashes. The outdoor unit shows its code on a panel behind a detachable door. Residential wall units have their own indications, set out in the model's operation manual.
What does alarm code 03 mean on a Hitachi?
Hitachi lists 03 as "Communication: Operational Irregularities between Indoor and Outdoor". The indoor and outdoor units have lost communication, so check the outdoor unit has power and then call an engineer to check the wiring between the units.
What does alarm code 08 mean on a Hitachi?
08 is "Cycle: Increase in Discharge Gas Temperature", which Hitachi also describes as when the temperature of the compressor's discharge is too high. It is a refrigerant circuit fault for an engineer to investigate.
Are E01, F01 and P01 Hitachi error codes?
We could not find those codes in any Hitachi document. Hitachi's published alarm codes are two characters, such as 01, 02 and b0, so check the code against your model's own manual rather than a generic list.
How do I reset a Hitachi air conditioner alarm?
Hitachi's manual does not treat a reset as a fix. Check the main power, fuse and breaker, the outdoor unit's airflow and the filters, then contact your installer with the model, the problem and the alarm code if it stays or returns.
Getting a Hitachi system fixed
A Hitachi alarm code tells an engineer where to start. If yours will not clear, our air conditioning repair team can diagnose it, and planned air conditioning maintenance keeps filters, coils and fans from causing the faults in the first place.
Last updated: 4 November 2026
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.