Daikin VRV IV RXTQ-TA / RXTQ-TB error code P4
Radiation fin thermistor abnormality, warning
Which models this applies to. Outdoor unit
Quick answer
On Daikin VRV IV RXTQ-TA / RXTQ-TB, P4 is a fault. It means radiation fin thermistor abnormality, warning. A first thing to check: A failed radiator fin thermistor.
- Applies to
- Daikin VRV IV RXTQ-TA / RXTQ-TB
- Daikin VRV IV RXTQ heat pump codes · Heat Pump
- Type of code
- Fault
- Urgency: Worth keeping an eye on
- First safe check
- Check the connector at the heat sink thermistor, which is disturbed during any inverter board service.
What P4 means on this model
The thermistor on the inverter heat sink has reported a fault. The operation lamp stays lit and the system can keep operating, but the unit has lost its most accurate heat sink reading and is relying on a less direct protection. It is the same sensor that feeds the L4 over-temperature shutdown.
Symptoms you will notice
- Outdoor unit shows P4 with the operation lamp lit
- The system may still heat or cool
- The unit runs but reports heat conditions less accurately
- The fault appeared after work on the inverter board
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 radiator fin thermistor
- A loose or disconnected connector at the thermistor
- A wiring fault at the sensor
- A thermistor that has been damaged during board service
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 the connector at the heat sink thermistor, which is disturbed during any inverter board service.
- Check that the thermistor is still attached to the heat sink and has not been knocked off.
Do not do these
- ×Do not ignore P4 because the system keeps running. The same sensor feeds the protection that produces the over-temperature shutdown, and losing it weakens that protection.
- ×Do not work on the inverter board with the power switch on.
When to call a technician
No call needed yet, but write it down
Note the date and the exact code, and watch whether it comes back. If it turns into a repeat fault or starts affecting performance, that is when it becomes worth a technician.
- 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
Radiator fin 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.