EC on a Daikin Altherma LT: Domestic hot water temperature too high

What it means

The manual says: Domestic hot water temperature too high.

Part involved: DHW tank temperature.

When it shows: The error is generated in case the domestic hot water temperature rises above 89°C.

Likely causes:

• Malfunction of the domestic hot water tank thermistor [R5T]; Incorrect parameters on the solar pump station.

Is it safe?

The manual does not say whether the heat pump stops.

Resetting itself: unknown.

Manual reset: Reset via the remote controller (Inspection/Test button) after the cause is fixed; some codes need a manual reset of the remote-controller memory (service manual section 1.4).

What you can check

• Read the full error code shown on the user interface 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).

What the engineer will check

• Follow the service-manual troubleshooting flow chart for this code: check malfunction of the domestic hot water tank thermistor [R5T]; check incorrect parameters on the solar pump station.

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

1 owner and engineer report mentions this.

• Hot water not hot enough on the Altherma LT (low temperature split): 1 report

Sources

• Service Manual ALTHERMA ERHQ006~008BAV3 / ERLQ006~008BAV3(9) / EKHBH(X)008BA (ESIE10-02) ↗ · ESIE10-02 · page 151 · Reviewed 23 September 2026

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

Reviewed: 23 September 2026