U8-05 on a Daikin Altherma: File malfunction

What it means

The manual says: File malfunction.

Part involved: user interface / room thermostat.

When it shows: File malfunction.

Likely causes:

• Connected USB/SDcard to update the user interface or upload e‑configuration data CANNOT be read because wrongly formatted, or the file config.cfg CANNOT be found on the USB/SDcard.

Is it safe?

The heat pump keeps running.

Resetting itself: no.

Manual reset: Manual reset via the 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 any room thermostat/controller display is lit and its batteries (if battery-powered) are not flat; check thermostat and schedule settings.
• 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.
• If heating/hot water has stopped, the operation manual lets the user confirm on the Malfunctioning screen whether the backup/booster heater may take over as emergency heating (much higher running cost) until the installer attends.

What the engineer will check

• Remove the USB/SDcard from the user interface. ; | Troubleshooting.

Who to ask for: Heat pump installer (Daikin-trained).

Certification: None specific; MCS-certified installer recommended.

What you might notice

• Controller / thermostat problem
• No heating

What owners and engineers report

13 owner and engineer reports mention this.

• No heating on the Altherma: 7 reports
• Controller / thermostat problem on the Altherma: 6 reports

Sources

• Service manual Daikin Altherma 3 M EBLA/EDLA04~08E (ESIE22-09) ↗ · ESIE22-09 · page 75 · Reviewed 23 September 2026

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

Reviewed: 23 September 2026