AH-00 on a Daikin Altherma: Tank disinfection function not completed correctly
Short answer
On a Daikin heat pump, AH-00 means: Tank disinfection function not completed correctly. The heat pump keeps running.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Tank disinfection function not completed correctly.
Part involved: tank disinfection function.
When it shows: Disinfection setpoint is NOT reached within 6 hours or NOT kept for the required time.
Likely causes:
- Large quantity of hot water has been tapped during/before disinfection.; ▪ Backup heater is restricted during disinfection, ▪ Backup heater NOT allowed.; Faulty booster heater settings.
Is it safe?
| Does the heat pump stop? | No |
|---|---|
| Severity | Warning |
The heat pump keeps running.
Resetting itself: yes.
Manual reset: Automatic reset when disinfection is completed.
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.
- Check the domestic hot water / programme schedule and settings on the user interface (Daikin notes AH-00 can be caused by large hot-water draws or stopping the tank during disinfection).
- Daikin documents this code as resetting automatically once the condition clears; if it keeps coming back, contact 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
- hours or NOT kept for the required time. Unit will NOT stop operating. Automatic reset when disinfection is completed. ; Check when the disinfection is scheduled. Schedule it when there is little chance that water will be tapped so that the disinfection can finish in time. ; Check the backup heater settings [2‑00] to [2‑04] and [4‑00]. . ; Check the domestic hot water tank and booster heater related settings. . ; | Troubleshooting.
Who to ask for: Heat pump installer / heating engineer.
Certification: G3 unvented hot water competence for cylinder safety components.
What you might notice
What owners and engineers report
5 owner and engineer reports mention this.
- Hot water not hot enough on the Altherma: 5 reports
Sources
- Service manual Daikin Altherma 3 M EBLA/EDLA04~08E (ESIE22-09) ↗ · ESIE22-09 · page 35 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026