Daikin Heat Pump Error Code C5

C5 indicates an abnormality with the indoor heat exchanger thermistor 2, identified as R3T. The unit has detected that this sensor is either disconnected or shorted while the system was running. Because the PCB cannot read a valid temperature from the coil, the unit shuts down to prevent potential damage. A technician needs to test the thermistor resistance and inspect the wiring to locate the fault.

The unit will typically shut itself down when C5 is active, which is the intended protective behavior. Attempting to force the system to run without a valid thermistor reading could result in uncontrolled coil temperatures, potential freeze-up, or refrigerant issues. It is best to leave the unit off until the fault is diagnosed and repaired.

If only the R3T thermistor needs replacement, parts typically cost in the range of $15 to $60 depending on the model, with labor adding $75 to $200 depending on your location and the technician called. If the fault turns out to be a damaged wiring harness or a failed PCB, total repair costs can rise to the $300 to $700 range or more. Getting a diagnosis before authorizing parts replacement will help avoid unnecessary expenses.

A knowledgeable DIYer can inspect the thermistor connector and wiring for obvious damage and reseat loose connectors without specialized tools. However, testing the thermistor resistance accurately requires a multimeter and access to the resistance reference table for the specific model. Replacing the thermistor or PCB involves working inside the unit and should be done by someone comfortable with appliance repair. If you are unsure, a licensed HVAC technician is the safest option.

A power reset may temporarily clear the fault code and allow the unit to restart, but if the underlying problem with the R3T thermistor or wiring persists, the C5 error will return once the unit is running again. Resetting without repairing is not a long-term solution and may make intermittent faults harder to diagnose.