If your Daikin VRV system is showing error code U5, an indoor unit has stopped communicating with its remote controller.
Of the faults on a VRV system, this is one of the least alarming — and one of the most likely to be misdiagnosed as something else, because of how it presents.
U5 is not U4
Worth establishing immediately, because the codes look similar and lead to different places.
| Code | The link that failed |
|---|---|
| U4 | Between indoor units and outdoor units — the main control network |
| U9 | Between indoor and outdoor units within the same system |
| U5 | Between a remote controller and its indoor unit |
U5 is one level down from the others. It concerns the wiring between the wall controller and the unit it operates, not the network linking equipment together.
That makes it both less serious and much cheaper.
Why it arrives as a comfort complaint
This is the practical reason to know about it.
From an occupant’s point of view, the controller looks perfectly normal. It powers up, it responds to touch, it displays a setpoint. It simply has no effect on the room.
So it gets reported as “the air conditioning in this office does not work properly” — and whoever investigates finds an indoor unit that is mechanically fine and a controller that appears fine. The fault is in the connection between them.
Meanwhile the unit carries on running whatever instruction it last received, which may be nothing at all, or may be conditioning an empty room through the weekend.
How urgent is it?
Low to moderate. Nothing is being damaged. No refrigerant is escaping, no compressor is at risk, and there is no safety concern.
The costs are comfort and energy. A zone that cannot be controlled is either generating complaints or quietly conditioning space nobody is using.
What it typically costs
Low — usually among the cheapest faults on a VRV system.
Most cases resolve to controller wiring or terminations, which is a technician visit rather than a part.
A replacement remote controller is a modest component, and unlike most indoor unit work the access is straightforward — it is on a wall at head height rather than above a ceiling.
What causes it
- Damaged or disconnected controller wiring — often during partition or ceiling work
- Loose or corroded terminals at either end
- Failed remote controller
- Indoor unit PCB fault at the receiving end
- Incorrect wiring following work on the controls
- Electrical interference — Daikin documentation notes that intermittent transmission faults where the system stops and restarts after a few minutes can be caused by electrical noise from equipment other than the air conditioning
That last one is worth remembering if your U5 comes and goes rather than staying present.
What happens if you leave it
The zone stays uncontrolled.
Depending on what instruction it was last given, that means either a room nobody can adjust, or a unit conditioning space continuously — including nights and weekends — with no way to stop it from the wall.
Neither damages equipment. Both cost money, one in complaints and one in energy.
What we check
- Confirm which zone and which controller are affected.
- Test the remote controller for correct operation.
- Inspect controller wiring between the controller and indoor unit.
- Check terminations at both ends for looseness and corrosion.
- Verify wiring is correct, particularly if work has been done recently.
- Look for interference sources if the fault is intermittent rather than constant.
- Test the indoor unit PCB once the controller and wiring are confirmed sound.
What you can tell us before we arrive
- Which zone? Speeds up access.
- Does the controller display normally? A blank controller and a live one with no effect point differently.
- Is it constant or intermittent? Intermittent suggests interference or a marginal connection.
- Has there been partition, ceiling or electrical work? A common origin.
- Is the unit running constantly, or not at all? Tells us what state it is stuck in.
Related codes
- U4 — Transmission between indoor and outdoor units. The main control network, and more serious.
- U9 — Transmission within the same system. Related but a different link again.
- A6 — Indoor fan motor fault. Another reason a zone stops conditioning, worth ruling out.
Cheap to fix, easy to miss
We are certified on Daikin, Mitsubishi and LG VRF platforms, and we service systems we did not install.
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Related codes
Error U4 means your indoor and outdoor units stopped communicating. The most frequently seen Daikin VRV fault, and usually one of the cheaper ones to put right.
Error U9 is a transmission error between indoor and outdoor units within the same system. Related to U4 but not the same code — and it is diagnosed differently.
Error A6 is an indoor fan motor fault. It covers six distinct conditions — from a physically locked motor to simply low airflow — with very different repairs.
Frequently asked questions
What does error code U5 mean on a Daikin VRV system?
A transmission error between the remote controller and the indoor unit. The controller and the unit it operates have stopped exchanging data, so instructions set on the wall are no longer reaching the equipment serving that zone. The unit itself is usually working perfectly.
Is U5 the same as U4?
No. U4 concerns communication between indoor and outdoor units — the main control network. U5 is one level down, between a remote controller and its indoor unit. Different wiring, different diagnosis, and U5 is generally much less serious.
Will my air conditioning still run with a U5 error?
Often yes, on whatever setting it last received. What you lose is control. Occupants can adjust the controller and nothing happens, which is why this typically arrives as a comfort complaint rather than a reported fault. The unit runs on whatever it was last told.
What causes a U5 communication error?
Damaged or disconnected controller wiring, loose or corroded terminals, a failed remote controller, an indoor unit PCB fault, or incorrect wiring after work on the controls. Damage during ceiling or partition work is a frequent origin. Electrical interference is also a recognised cause.
Can electrical noise cause a U5 error?
Yes. Daikin documentation notes that intermittent transmission faults where the system stops and restarts after a few minutes can result from electrical noise generated by equipment other than the air conditioning system. If your fault comes and goes rather than staying present, that is worth mentioning to us.
How much does a U5 error cost to fix?
Usually among the cheapest faults on the system. Most cases resolve to controller wiring or terminations, which is a technician visit. A replacement remote controller is a modest part with straightforward access compared to ceiling equipment. It sits on a wall rather than above a ceiling tile.