UA-22 on a Daikin Altherma: Communication problem between control box and option box
Short answer
On a Daikin heat pump, UA-22 means: Communication problem between control box and option box. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Communication problem between control box and option box.
Part involved: inter-unit communication / PCB combination.
When it shows: Communication between control box and option box has failed.
Likely causes:
- Wiring between control box and option box is too long.; Faulty extension PCB A4P.; Faulty wiring between control box and option box.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: no.
Manual reset: Manual reset via user interface.
What you can check
- Read the full error code and sub-code shown on the user interface (Malfunctioning screen; press the help button for Daikin's long description) and note it, with the date/time, for your installer.
- Do NOT bleed radiators while an error/malfunction symbol is displayed: Daikin operation manuals warn refrigerant may have leaked into the water circuit - ventilate and call your installer.
- If heating/hot water has stopped, the operation manual lets the user confirm on the Malfunctioning screen whether the backup/booster heater may take over as emergency heating (much higher running cost) until the installer attends.
What the engineer will check
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
13 owner and engineer reports mention this.
- No heating on the Altherma: 7 reports
- Controller / thermostat problem on the Altherma: 6 reports
Sources
- Service manual Daikin Altherma Monobloc CA EBLQ/EDLQ05-07CAV3 (ESIE15-08B) ↗ · ESIE15-08B · page 40 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026