Fujitsu Mini-Split Code 42
Soft lockoutShown as: OPERATION lamp blinks 4 times, TIMER lamp blinks 2 times, ECONOMY lamp blinking continuously
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