UA on a Daikin heat pump: Communication error between outdoor unit and indoor unit
Short answer
On a Daikin heat pump, UA means: Communication error between outdoor unit and indoor unit. The manual does not say whether the heat pump stops. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 2 sources
What it means
On the Altherma HT (high temperature split)
The manual says: Communication error between outdoor unit and indoor unit.
Part involved: inter-unit communication / PCB combination.
Likely causes:
- Excess of connected indoor units; Defect of outdoor unit PC board (A1P); Mismatching of the type of indoor and outdoor unit; Setting of outdoor PC board was not conducted after replacing to spare parts PC board.
On the Altherma LT (low temperature split)
The manual says: Combination error (indoor outdoor unit) or spare parts PCB.
Part involved: inter-unit communication / PCB combination.
Is it safe?
On the Altherma HT (high temperature split)
| Does the heat pump stop? | Not stated |
|---|---|
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
Resetting itself: unknown.
On the Altherma LT (low temperature split)
| Does the heat pump stop? | Not stated |
|---|---|
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
Resetting itself: unknown.
Manual reset: Reset via the remote controller (Inspection/Test button) after the cause is fixed; some codes need a manual reset of the remote-controller memory (service manual section 1.4).
What you can check
- Read the full error code shown on the user interface and note it, with the date/time, for your installer.
What the engineer will check
On the Altherma HT (high temperature split)
- Follow the service-manual troubleshooting flow chart for this code: check excess of connected indoor units; check defect of outdoor unit PC board (A1P); check mismatching of the type of indoor and outdoor unit; check setting of outdoor PC board was not conducted after replacing to spare parts PC board.
Who to ask for: Heat pump installer (Daikin-trained).
Certification: None specific; MCS-certified installer recommended.
On the Altherma LT (low temperature split)
- See Daikin service manual for this generation.
Who to ask for: Heat pump installer (Daikin-trained).
Certification: None specific; MCS-certified installer recommended.
What you might notice
What owners and engineers report
1 owner and engineer report mentions this.
- No heating on the Altherma LT (low temperature split): 1 report
Sources
- Service Manual Daikin ALTHERMA HT ERSQ/ERRQ 011-016 AA V1/Y1 + EKHBRD (ESIE09-08C) ↗ · ESIE09-08C · page 220 · Reviewed 23 September 2026
- Service Manual ALTHERMA ERHQ006~008BAV3 / ERLQ006~008BAV3(9) / EKHBH(X)008BA (ESIE10-02) ↗ · ESIE10-02 · page 141 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026