Daikin VRV IV RXTQ-TA / RXTQ-TB error code U5
Transmission error between the controller and the indoor unit
Which models this applies to. System
Quick answer
On Daikin VRV IV RXTQ-TA / RXTQ-TB, U5 is a fault. It means transmission error between the controller and the indoor unit. A first thing to check: A loose or disconnected controller cable.
- 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 the controller cable at both ends, and at any point where the cable has been run through a wall or a door frame.
What U5 means on this model
The link between the room controller and its indoor unit has failed, so usually one zone is affected rather than the whole system. On a wireless controller the same code covers a pairing or receiver problem rather than a wiring one.
Symptoms you will notice
- Indoor unit shows U5 and the zone does not respond
- Only one zone is affected
- The controller shows no communication or no unit
- The fault appeared after a controller was moved or replaced
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 loose or disconnected controller cable
- A failed controller or indoor unit interface
- A damaged controller cable run, often at a corner or a door frame
- A wireless controller that has lost its pairing or its receiver faulted
- A controller installed outside its rated cable length
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 controller cable at both ends, and at any point where the cable has been run through a wall or a door frame.
- Note whether the affected zone is a single room, which narrows it to the controller run.
- For a wireless controller, check the pairing and whether the receiver in the unit is responding.
Do not do these
- ×Do not run the controller cable alongside mains power without separation.
- ×Do not assume the whole indoor unit has failed because one zone is unresponsive. U5 is the controller link, not the unit.
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.
Checking and reseating a controller connector is reasonable for a homeowner comfortable with that. Board level work is a technician job.
What it costs to fix
Parts
Controller cable $20 to $80. Remote controller $120 to $300. Receiver $80 to $200.
Labor
One to two hours to trace and fix.
DIY or technician
Checking and reseating a controller connector is reasonable for a homeowner comfortable with that. Board level work is 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.