81-07 on a Daikin Altherma: Exit water temperature thermistor after tank valve abnormality
Short answer
On a Daikin heat pump, 81-07 means: Exit water temperature thermistor after tank valve abnormality. 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: Exit water temperature thermistor after tank valve abnormality.
Part involved: water valves (diverter/mixing/tank/bypass).
When it shows: Mixed leaving water thermistor (after tank) is out of range.
Likely causes:
- Faulty mixed leaving water thermistor.; Faulty hydro extension PCB.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: yes.
Manual reset: Automatic reset. EPRA14~18D + ETSH/X(B)16P30+50E Daikin Altherma 3 H HT ECH₂O 3 | Troubleshooting.
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 heating-system water pressure reading on the gauge/display: Daikin operation manuals ask users to check it is above 1 bar. If it is below that, report it to your installer (do not open the unit).
- 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.
- 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
- Perform a check of the mixed leaving water thermistor. ; Perform a check of the hydro extension PCB.
Who to ask for: Heat pump installer / heating engineer.
Certification: None specific for water-side checks; MCS-certified installer recommended.
What you might notice
What owners and engineers report
11 owner and engineer reports mention this.
- No heating on the Altherma: 7 reports
- Keeps stopping / cutting out on the Altherma: 2 reports
- No hot water on the Altherma: 2 reports
Sources
- Service manual Daikin Altherma 3 H HT ECH2O EPRA14-18D + ETSH/ETSX(B)16P30/50E (ESIE22-11A) ↗ · ESIE22-11A · page 26 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026