Daikin VRV IV RXTQ-TA / RXTQ-TB error code C5
Indoor heat exchanger gas pipe thermistor abnormality
Which models this applies to. Indoor unit
Quick answer
On Daikin VRV IV RXTQ-TA / RXTQ-TB, C5 is a fault. It means indoor heat exchanger gas pipe thermistor abnormality. A first thing to check: A failed thermistor.
- Applies to
- Daikin VRV IV RXTQ-TA / RXTQ-TB
- Daikin VRV IV RXTQ heat pump codes · Heat Pump
- Type of code
- Fault
- Urgency: Book a technician
- First safe check
- Confirm the thermistor is clipped to the pipe and the wire is undamaged.
What C5 means on this model
The thermistor on the gas side of the indoor coil, the vapour line, is not reporting a usable value. The control needs it for the superheat calculation and will not run the unit without it.
Symptoms you will notice
- Indoor unit shows C5 and stops
- The unit will not heat or cool
- The unit runs erratically and will not hold setpoint
- The fault follows a service on the indoor unit
Common causes
The code tells you what the control detected, not which part failed. These are the causes we see most often, roughly in order of likelihood:
- A failed thermistor
- A loose or broken wire to the thermistor
- A disturbed connector at the thermistor
- A clip that has come loose off the pipe
- Thermistor resistance out of range
What you can safely check
These are homeowner-level checks. None of them need you to open a live electrical compartment or work on gas.
- Confirm the thermistor is clipped to the pipe and the wire is undamaged.
- Check the connector at the thermistor.
- Compare the resistance against the pipe temperature using the chart in the manual.
Do not do these
- ×Do not leave a thermistor hanging off the pipe rather than clipped to it, because the control has no way to know the reading is not the pipe temperature.
- ×Do not work on the connector with the power switch on.
When to call a technician
Worth scheduling, and worth your own checks first
You can usually keep living with this for a short while, but it will not fix itself. Do the safe checks below first, because a tripped switch or a blocked airflow is a five-minute fix that would otherwise cost you a service call.
- The refrigerant circuit is sealed and legally requires licensed handling. Opening it without certification releases refrigerant and can put the whole system in violation of regulation, so a low-pressure or high-pressure fault on this equipment is a call-out, not a weekend job.
- If the appliance has stopped mid-cycle, is making a noise you have not heard before, or smells burnt, stop reading here and call. Those are symptoms of something the fault code does not describe well enough.
A technician job.
What it costs to fix
Parts
Thermistor $30 to $90.
Labor
One to two hours to test and replace.
DIY or technician
A technician job.
Typical US part and labor ranges, 2026. They vary by region, model and contractor, so treat them as a planning figure, not a quote.
Scope of this code
- Code table
- Daikin VRV IV RXTQ heat pump codes
- Models in scope
- Daikin VRV IV RXTQ-TA / RXTQ-TB
- Checked
- Confirm on your own unit
- Find the model number on the data plate, then check this code in the service manual for that model. Manufacturers revise code tables between model years, and a revised board can renumber a fault.