Daikin Thermostat Error Codes

The reason for the incomplete operation of the thermostat can be a breakdown of the device itself, as the problems with the voltage in the power supply and not only. Below are the tables containing information about Daikin thermostats. In each table you will find information about different models of this brand: fault codes, its causes and repair methods.

Daikin CTXU25G2V1B Thermostat Error Codes

Error Cause
A1 Indoor unit PCB abnormality
PCB Freeze-up protection or high pressure control
A5 Fan motor or related abnormality
A6 Indoor heat exchanger thermistor abnormality
C4 Room temperature thermistor abnormality
C9 Humidity sensor abnormality
CC Outdoor unit PCB abnormality
E1 OL activation (compressor overload)
E5 Compressor lock
E6 DC fan lock
E7 Input overcurrent detection
E8 Discharge pipe temperature control
F3 High pressure control in cooling
F6 Compressor sensor system abnormality
H0 Damper abnormality
H1 Position sensor abnormality
H6 DC voltage / DC current sensor abnormality
H8 Outdoor air thermistor abnormality
H9 Discharge pipe thermistor abnormality
J3 Outdoor heat exchanger thermistor abnormality
J6 Liquid pipe thermistor abnormality
J8 Gas pipe thermistor abnormality
J9 Abnormal temperature in electrical box
L3 Temperature rise in radiation fin
L4 Output overcurrent
L5 Radiation fin thermistor abnormality
P4 Fan motor system abnormality / fan lock
P9 Heater wire abnormality
PA Humidification fan outlet thermistor abnormality / abnormal heater temperature
PH Insufficient gas
U0 Over voltage protection (OVP) / low voltage protection (LVP)
U2 Signal transmission error (indoor unit – outdoor unit)
Outdoor unit PCB abnormality or communication circuit abnormality
U4 Signal transmission error on outdoor unit PCB
U7 Incompatible power supply between indoor unit and outdoor unit
UA Incomplete setting for hose length


Daikin Mcquay Thermostat Error Codes

Fault code Description Cause for the fault
AU Auto Damper Control setup indicator damper is in “automatic” mode.
Au Auto HP/E Control setup indicator heat pump electric is in automatic changeover mode (HP/E).
bo Brown Out or Low Voltage Brown Out – Control monitors input voltage to prevent relay chattering. When voltage drops below 17 VAC, outputs are disabled until voltage input increases to 20 VAC or greater.
bY HP/E Bypass Control setup indicator, electric heat is bypassed when OCS > 40°.
CE LUI Communication Communication Error, connection between LUI and control board.
CL Damper Closed Control setup indicator damper is in “closed” mode.
CF Coil Freeze Protection Indoor coil is < 32° for at least 5 minutes. Compressor and outdoor fan stop and indoor fan continues to run for active defrost. Protection feature and the displayed code are dismissed when indoor coil temperature rised above 49°F.
Hi Temperature Limiting Hi Room Room Temperature Display Indication ONLY – Indoor air temperature is 5° above Maximum set point. Displayed code is dismissed when IAS temperature is < 5° from Max set point as adjusted in the Set Up Mode.
LA Low Ambient Lockout Unit is in cooling mode and outdoor air < 25°. Compressor will cut out.
m Slave Unit Set to be Controlled by a Master Unit When slave unit jumper for Control Select is positioned over SEC, slave unit is set to be controlled by a Master control unit.
LC Control Lockout – Lockout Mode Displays for 5 seconds when any button is pushed when in the “lockout mode”. To initiate, hold MODE button for 10 seconds.
Lo Temperature Limiting Low Room Room Temperature Display Indication ONLY – Indoor air temperature is < 5° below minimum set point. Displayed code is dismissed when IAS temperature is > 5° from Minimum set point as adjusted In the Set Up Mode.
nL Control Lockout – Normal Control Displays for 5 seconds to confirm normal mode of operation when control lock out turned ofT. Initiate by holding MODE button for 10 sec.
rF Room Freeze Protection Room temperature <41°. Damper closes (Premium board) and unit goes into heat mode.
Sh Jumper Status Missing Shunt or not properly installed.
El Indoor Air Sensor Indoor Air Thermister Failure. Sensor missing or Short.
E2 Indoor Coil Sensor Indoor Coil Thermister Failure. Sensor missing or Short.
E3 Outdoor Coil Sensor Outdoor Coil Thermister Failure. Sensor missing or Short.
E4 Outdoor Air Sensor Outdoor Air Thermister Failure. Sensor missing or Short.
E5 Heat Fan Lock Out Sensor Heat Fan Lock Out Sensor Failure, missing, short on control board or heating medium >250°F. Check for installation/connection of HFLO sensor. Should be on coil return line.


Daikin FTXN09KEVJU Thermostat Error Codes

Error Codes Description
System 0 Normal
uo Refrigerant shortage
U2 Low-voltage detection or over-voltage detection
U4 Signal transmission error (between indoor unit and outdoor unit)
UA Unspecified voltage (between indoor unit and outdoor unit)
Indoor A1 Indoor unit PCB abnormality
Unit A5 Freeze-up protection control or heating peak-cut control
A6 Fan motor (DC motor) or related abnormality
C4 Indoor heat exchanger thermistor or related abnormality
C9 Room temperature thermistor or related abnormality
Outdoor E1 Outdoor unit PCB abnormality
Unit E5 OL activation (compressor overload)
E6 Compressor lock
E7 DC fan lock
ES Input overcurrent detection
EA Four-way valve abnormality
F3 Discharge pipe temperature control
F6 High pressure control in cooling
HO Compressor system sensor abnormality
H6 Position sensor abnormality
HS DC voltage / current sensor abnormality (09/12 class only)
H9 Outdoor temperature thermistor or related abnormality
J3 Discharge pipe thermistor or related abnormality
J6 Outdoor heat exchanger thermistor or related abnormality
L3 Electrical box temperature rise
L4 Radiation fin temperature rise
L5 Output overcurrent detection
P4 Radiation fin thermistor or related abnormality


Daikin Altherma Thermostat Error Codes

Symptom Possible Cause Action
Cool ON or Heat ON is displayed, but no warm or cool air is coming from the registers. 1. The heating equipment turns on the fan when the furnace has warmed up to a setpoint. 1. Wait one minute after seeing the ON icon and then check the registers.
2. Heating or cooling equipment is not operating. 2. Check Heating and Cooling system.
“Service“ Flashing on and off. Control EEPROM write error. Press any key and Check / Re-enter Setup Choices.
“Service” solid on and in temperature display. Indoor temperature sensor open or shorted Replace Control
Display will not come on. 1. Blown fuse or tripped circuit breaker. 1. Replace fuse or reset breaker.
2. Furnace power switch OFF. 2. Turn switch to ON.
3. Furnace blower compartment door or panel loose or not properly installed. 3. Replace door panel in proper position to engage safety interlock or door switch.
Temperature display is incorrect. Temperature display needs calibration. Calibrate Sensor.
Cannot set Heating setpoint above 80 degrees Deadband between Heating and Cooling set to high Decrease Deadband setting .
Temperature setting will not change. (Example: Cannot set heating higher or cooling lower). 1. Upper and/or lower temperature limits were reached. 1. Check the temperature setpoints:
Heating limits are 40 – 85F.
Cooling limits are 65 – 90F.
2. “Keypad locked” is displayed on LCD. 2. Unlock keypad – press Up+Down arrow together until icon disappears.