Daikin VRV IV RXTQ-TA / RXTQ-TB error code A0
Indoor unit external protection device abnormality
Which models this applies to. Indoor unit
Quick answer
On Daikin VRV IV RXTQ-TA / RXTQ-TB, A0 is a fault. It means indoor unit external protection device abnormality. A first thing to check: An outdoor unit protection device has operated.
- Applies to
- Daikin VRV IV RXTQ-TA / RXTQ-TB
- Daikin VRV IV RXTQ heat pump codes · Heat Pump
- Type of code
- Fault
- Urgency: Needs attention soon
- First safe check
- Read the outdoor unit codes before touching the indoor unit, because A0 is the indoor unit repeating an outdoor fault.
What A0 means on this model
The indoor unit is repeating a protection trip that happened in the outdoor unit, so the actual fault is outdoors. On a wired controller the sub-code A0-01 points at the outdoor protection circuit.
Symptoms you will notice
- Indoor unit shows A0 and the system stops
- The indoor unit is fine and the fault is actually in the outdoor unit
- System shuts down during a heat demand
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:
- An outdoor unit protection device has operated
- The outdoor high or low pressure switch, sensor or inverter protection has tripped
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.
- Read the outdoor unit codes before touching the indoor unit, because A0 is the indoor unit repeating an outdoor fault.
- Check the refrigerant pressure and the outdoor unit protections listed in the outdoor code that accompanies it.
Do not do these
- ×Do not start replacing indoor unit parts on A0. The indoor unit is the messenger, not the fault.
- ×Do not leave the power switch on while connecting or disconnecting connectors, which is the standing caution throughout this service manual.
When to call a technician
Book a technician, do not keep resetting it
This fault will not clear on its own. Every power cycle gives the control one more failed attempt, and repeated attempts are what turn a cheap part replacement into a seized or contaminated system.
- 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. The code is only meaningful once the outdoor unit has been read.
What it costs to fix
Parts
Depends on the outdoor part that actually tripped. Indoor unit PCB $200 to $450.
Labor
One to two hours to trace the A0 to the outdoor protection that operated.
DIY or technician
A technician job. The code is only meaningful once the outdoor unit has been read.
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.