Heat pumps · Error codes · Daikin
C1-11Daikin · Altherma 3 WS (water source)
C1-11 on a Daikin Altherma 3 WS: ACS communication malfunction
Short answer
On a Daikin heat pump, C1-11 means: ACS communication malfunction. The manual does not say whether the heat pump stops. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: ACS communication malfunction.
Part involved: inter-unit communication / PCB combination.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
Resetting itself: unknown.
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.
What the engineer will check
- See Daikin service manual for this generation (not public).
Who to ask for: Heat pump installer (Daikin-trained).
Certification: None specific; MCS-certified installer recommended.
What you might notice
Sources
- Installer reference guide Daikin Altherma 3 WS EWSAH/EWSAX-UD9W (4P675765-1A) ↗ · 4P675765-1A · page 249 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026