Daikin VRV IV RXTQ-TA / RXTQ-TB error code U3
Check operation not executed
Which models this applies to. System
Quick answer
On Daikin VRV IV RXTQ-TA / RXTQ-TB, U3 is a fault. It means check operation not executed. A first thing to check: The check operation has not been performed since installation.
- 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 with the installer whether the check operation has been carried out, since it is a commissioning step performed with the commissioning tools.
What U3 means on this model
The installer check operation has not been carried out, so the system will not run. This is a commissioning code rather than a fault, and it most often appears on a new installation or after field settings were changed. It needs the manufacturer commissioning tools.
Symptoms you will notice
- Outdoor unit shows U3 and the system will not start
- The system is newly installed or newly reconfigured
- The system worked before and stopped after field settings were changed
- The system is being handed over and has not been commissioned
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:
- The check operation has not been performed since installation
- Field settings were changed and the check operation was not repeated
- A system that has been stored or powered off before commissioning
- A partially completed commissioning after a repair
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 with the installer whether the check operation has been carried out, since it is a commissioning step performed with the commissioning tools.
- Check whether any field settings were changed recently, because that invalidates a previous check operation.
Do not do these
- ×Do not try to force the system past this code from the room controller. The check operation is a commissioning procedure performed with the manufacturer tools and it is what verifies the settings are safe.
- ×Do not assume the system is broken. U3 usually means it has not been switched on properly rather than that anything has failed.
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 commissioning technician job. The check operation needs the manufacturer tools.
What it costs to fix
Parts
None expected.
Labor
One to three hours for the commissioning technician to run the check operation.
DIY or technician
A commissioning technician job. The check operation needs the manufacturer tools.
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.