Fujitsu Mini-Split: 4 Flashes
A Fujitsu mini-split LED pattern starting with 4 flashes matches 3 documented codes: 41, 42, 44. Watch the full pattern (short vs. long flashes) to tell them apart — all 3 are explained below.
Code 41: Indoor room thermistor error
Indoor room thermistor error. The room temperature sensor in the indoor unit has read an impossible temperature, meaning it is open or shorted.
Manual wording: “Indoor Room Thermistor Error - Room temperature thermistor detected an abnormal temperature.”
Documented for: RGLX, RL2/RLS2/RLS3/RLB/RLXB wall mounted, RLF/RLF1 multi-zone
Likely causes, most common first
- Open or shorted room temperature thermistor
- Thermistor resistance out of specification
- Failed indoor controller PCB
What you can safely check yourself
- Turn the power off at the breaker for about 5 minutes and back on to see whether the code clears
When to call a technician
The room thermistor is behind the indoor unit's front panel and has to be ohm-checked against Fujitsu's resistance table. Have a technician replace it.
A Fujitsu mini-split throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Source
- 410A Mini-Split Troubleshooting Guide (Part # 6-26-FG2020 Rev. 5/2019) (Fujitsu General America, Inc., All R410A Halcyon mini-splits: RGLX, RL2/RLS3/RLS3H/RLS3Y/RLB/RLXB/RLXEH wall mounted, RLF/RLF1 multi-zone indoor units, RLXFZ multi-zone outdoor units, RML/RMLQ, RULX/RSLX universal-mount, RCLX cassettes) · checked 2026-08-25
Code 42: Indoor heat exchanger
Indoor heat exchanger (pipe) thermistor error. The evaporator coil pipe sensor has read an abnormal temperature, meaning it is open or shorted.
Manual wording: “Indoor Heat Ex. (Pipe) Thermistor Error - Evaporator pipe thermistor detected an abnormal temperature.”
Documented for: RGLX, RL2/RLS2/RLS3/RLB/RLXB wall mounted, RLF/RLF1 multi-zone
Likely causes, most common first
- Open or shorted indoor pipe thermistor
- Thermistor resistance out of specification
- Failed indoor controller PCB
What you can safely check yourself
- Turn the power off at the breaker for about 5 minutes and back on to see whether the code clears
When to call a technician
The pipe thermistor clips onto the evaporator coil behind the indoor unit's casing. Replacing it is a technician's job.
A Fujitsu mini-split throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Source
- 410A Mini-Split Troubleshooting Guide (Part # 6-26-FG2020 Rev. 5/2019) (Fujitsu General America, Inc., All R410A Halcyon mini-splits: RGLX, RL2/RLS3/RLS3H/RLS3Y/RLB/RLXB/RLXEH wall mounted, RLF/RLF1 multi-zone indoor units, RLXFZ multi-zone outdoor units, RML/RMLQ, RULX/RSLX universal-mount, RCLX cassettes) · checked 2026-08-25
Code 44: Human sensor error
Human sensor error. The occupancy (human) sensor on the indoor unit is not responding correctly to the control board.
Manual wording: “Human Sensor error - Check if the connector connection and if cable is open”
Documented for: RGLX indoor units fitted with the human/occupancy sensor option
Likely causes, most common first
- Loose or removed human sensor connector
- Erroneous connection at the sensor plug
- Open sensor cable
- Failed sensor, or failed main PCB
What you can safely check yourself
- Turn the power off at the breaker for about 5 minutes and back on to see whether the code clears
When to call a technician
Diagnosing this requires continuity and 5 VDC checks at connector CN67 on the main board. That is technician work.
A Fujitsu mini-split throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Source
- 410A Mini-Split Troubleshooting Guide (Part # 6-26-FG2020 Rev. 5/2019) (Fujitsu General America, Inc., All R410A Halcyon mini-splits: RGLX, RL2/RLS3/RLS3H/RLS3Y/RLB/RLXB/RLXEH wall mounted, RLF/RLF1 multi-zone indoor units, RLXFZ multi-zone outdoor units, RML/RMLQ, RULX/RSLX universal-mount, RCLX cassettes) · checked 2026-08-25