EC-00 on a Daikin Altherma: Abnormal increase tank temperature

What it means

The manual says: Abnormal increase tank temperature.

Part involved: DHW tank temperature.

When it shows: Domestic hot water tank thermistor measures a too high temperature.

Likely causes:

• Increased water temperature due to an external heat source.; Faulty domestic hot water tank thermistor.; Faulty hydro PCB.

Is it safe?

The heat pump keeps running.

Resetting itself: yes.

Manual reset: Automatic reset.

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

• Check the water circuit for an external heat source. . ; Perform a check of the domestic hot water tank thermistor. . ; Perform a check of the hydro PCB. .

Who to ask for: Heat pump installer / heating engineer.

Certification: G3 unvented hot water competence for cylinder safety components.

What you might notice

• Hot water not hot enough
• Hot water too hot / scalding (incl. legionella cycle)

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 50 · Reviewed 23 September 2026

A code explains what the controller detected, not a confirmed root cause.

Reviewed: 23 September 2026