8F-00 on a Daikin Altherma: Abnormal increase outlet water temperature (DHW)
Short answer
On a Daikin heat pump, 8F-00 means: Abnormal increase outlet water temperature (DHW). 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: Abnormal increase outlet water temperature (DHW).
Part involved: DHW tank temperature.
When it shows: Outlet water after backup heater thermistor detects a too high temperature during domestic hot water without electrical heater.
Likely causes:
- Water flow is too low.; Faulty outlet water after backup heater thermistor.; Clogged water circuit.; Faulty water pump.; Faulty backup heater contactor(s).
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.
- 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).
- 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
- Check the water flow. . ; Perform a check of the outlet water after backup heater thermistor. . ; | Troubleshooting ; Check if the water circuit is clogged. . ; Perform a check of the water pump. . ; Perform a check of the backup heater contactor(s). .
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 29 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026