Daikin UA error code: indoor and outdoor unit combination fault
Daikin UA means the indoor and outdoor units are not a valid combination, too many heads are connected, or a replaced control board was not set. What each case looks like.
What this means
Daikin assigns UA to an improper combination of indoor and outdoor units. The paired models are not compatible, the number of connected indoor units is outside the outdoor unit's limit, the refrigerant types do not match, or a replacement control board was fitted without its combination setting being made.
Equipment and model context
Daikin split and multi-split systems that publish UA for an indoor and outdoor combination fault
- FTXS / RXS splits
- MXS / MXL multi-zone outdoor units
- matched FTXM indoor units
This meaning follows the Daikin malfunction code table for split and multi-split systems that list UA. SkyAir and VRV ranges assign UA-adjacent codes differently, so confirm the outdoor model and every connected indoor model before acting.
What you may notice
- UA appears at commissioning of a new or reworked system, or straight after a control board was replaced, and the system will not run.
- One or more indoor units do not start, or the system starts and then stops with UA on the controller.
Likely causes
- An indoor unit and outdoor unit that are not a rated pairing, or a mix of R-32 and R-410A equipment, have been connected together.
- More indoor units are connected to a multi-split outdoor unit than it is rated to carry, or a spare control board was fitted without the model or capacity setting being entered.
Diagnostic paths
UA on a newly assembled system
The equipment is new or newly combined, the indoor and outdoor units may have come from different kits or suppliers, and UA showed on the first test run.
The installer confirms every indoor model is a rated match for the outdoor unit, that the refrigerant types agree, and that the head count is within the outdoor unit's limit, then replaces or removes whatever does not fit.
UA immediately after a control board replacement
The system worked before a board failure, a replacement PCB was fitted, and UA appeared as soon as power was restored.
The technician makes the combination or capacity setting the replacement board needs, following the service procedure for that model, so the board knows which system it is controlling.
A Daikin outdoor unit expects to see indoor units it is rated to run, of a matching refrigerant, within a set count. UA is the control rejecting a set-up that falls outside those limits.
- Outdoor unit ratingDefines which indoor models and how many it supports
- Connected indoor unitsTheir models, count, and refrigerant type
- Control board settingTells a replacement PCB which system it runs
- Combination checkControl compares what is connected with what is allowed
- UA displayedThe connected set is outside the rated combination
| Situation | What is wrong | Resolution |
|---|---|---|
| Mixed kit at install | Indoor and outdoor units are not a rated pairing | Match to a combination Daikin publishes |
| Refrigerant mismatch | R-32 and R-410A equipment connected together | Use equipment of one refrigerant type |
| Too many heads | Indoor unit count above the outdoor limit | Remove heads until within the rating |
| After a board swap | Replacement PCB not set for the system | Enter the model or capacity setting per the service manual |
UA is a compatibility statement
Daikin publishes which indoor units each outdoor unit is designed to run, how many indoor units a multi-split outdoor can carry, and which refrigerant a given system uses. The control checks the connected equipment against those rules at start-up. UA is the result when the set-up breaks one of them: an indoor and outdoor unit that were never rated as a pair, a mix of R-32 and R-410A equipment, or a fifth head on an outdoor unit rated for four.
There is also a software side. When a control board is replaced, the new board is generic until it is told which model and capacity of system it is in. If that setting is skipped, the board cannot confirm the combination it is looking at, and it raises UA even though the physical equipment is a valid match.
None of the fixes are owner tasks
Each cause of UA is resolved at the equipment or the service menu. Correcting a mismatched pairing means changing an indoor or outdoor unit for one Daikin lists as compatible. A refrigerant mismatch means the incompatible unit is removed from the system entirely. Too many heads means disconnecting indoor units, with the pipe ends and wiring made safe, until the count is within the rating.
The board-setting case is a documented service procedure specific to the model, entered through the control after a PCB change. All of these involve refrigerant connections, low-voltage wiring, or a service menu that is not exposed to the user, so UA is handled by the installer or a Daikin technician rather than by the homeowner.
What to give the technician
Give the installer the outdoor model, every indoor model and its room, whether the equipment came from one kit or several, the refrigerant type marked on each unit, and whether a control board was recently replaced.
Safe homeowner checks
- Note whether UA appeared at first commissioning, after equipment was combined from different kits, or right after a control board was replaced.
- Write down the outdoor model and every indoor model with the room it serves, so the installer can check the combination against Daikin's data.
Is a reset appropriate?
A power cycle does not change the equipment combination or a missing board setting, so UA returns until the underlying mismatch is corrected. Resetting is not a fix for this code.
When to call a technician
- Changing paired equipment, removing indoor units from a multi-split, and making a replacement board's combination setting are all installer or technician tasks.
Questions people ask about this
Why does my new Daikin show UA?
The indoor and outdoor units are not a rated pairing, the refrigerant types do not match, or a multi-split has more heads connected than it is rated for. The installer needs to correct the combination.
UA started after a PCB replacement. What now?
A replacement control board is generic until it is told which system it controls. The technician makes the combination or capacity setting through the service procedure for that model, and UA clears.
Can I mix R-32 and R-410A Daikin units?
No. Connecting equipment of different refrigerant types is one of the situations Daikin reports as UA. A system has to use units of a single refrigerant type throughout.
Evidence recordHow this page was checked
service manual, official manufacturer support article · checked 2026-09-09
Every technical claim above was written from primary documentation held in the HVAC Bench evidence record: Daikin Comfort Technologies and Daikin Industries technical literature. Where a source limits a definition to certain models, test conditions, or product classes, that limit is repeated here rather than generalised.
- Documentation class
- service manual, official manufacturer support article
- Scope of the definition
- Daikin split and multi-split systems that publish UA for an indoor and outdoor combination fault
- Last checked
- 2026-09-09