Daikin VRV IV RXTQ-TA / RXTQ-TB error code C4
Indoor heat exchanger liquid pipe thermistor abnormality
Which models this applies to. Indoor unit
Quick answer
On Daikin VRV IV RXTQ-TA / RXTQ-TB, C4 is a fault. It means indoor heat exchanger liquid 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
- Check that the thermistor is still clipped to the pipe and that the wire is not pinched or cut.
What C4 means on this model
The thermistor clipped to the liquid side of the indoor coil is not reporting a value the control can use, so the unit has stopped rather than run on an unmeasurable coil temperature.
Symptoms you will notice
- Indoor unit shows C4 and stops
- The unit does not heat or cool at all
- The fault follows a coil cleaning or a drain pan service
- The thermistor or its clip has been disturbed
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 connector that has been disturbed during service
- Thermistor resistance out of range for the temperature it is reading
- A clip that has come loose so the sensor is no longer reading the pipe
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.
- Check that the thermistor is still clipped to the pipe and that the wire is not pinched or cut.
- Check the connector at the thermistor, which is disturbed on almost every coil service.
- Compare the measured resistance against the temperature the pipe is actually at, using the resistance chart in the manual.
Do not do these
- ×Do not clip the thermistor somewhere convenient rather than back on the pipe, because a thermistor reading air temperature will be trusted by the control as if it were valid.
- ×Do not leave the power switch on while disconnecting a thermistor.
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 once the coil is involved.
What it costs to fix
Parts
Thermistor $30 to $90. Indoor coil $250 to $600 if damaged during removal.
Labor
One to two hours to test and replace.
DIY or technician
A technician job once the coil is involved.
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.