Heat pumps · Error codes · Daikin
81-04Daikin · Altherma
81-04 on a Daikin Altherma: Leaving water temperature sensor not properly mounted
Short answer
On a Daikin heat pump, 81-04 means: Leaving water temperature sensor not properly mounted. The manual does not say whether the heat pump stops. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Leaving water temperature sensor not properly mounted.
Part involved: thermistor / pressure sensor.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
Resetting itself: unknown.
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.
- 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
- See Daikin service manual for this generation (not public).
Who to ask for: Heat pump engineer (Daikin-trained).
Certification: Electrical competence to BS 7671 for sensor/PCB wiring; F-gas if a refrigerant-side sensor must be replaced.
What you might notice
What owners and engineers report
9 owner and engineer reports mention this.
- No heating on the Altherma: 7 reports
- Intermittent fault on the Altherma: 2 reports
Sources
- Installer reference guide Daikin Altherma 3 WS EWSAH/EWSAX-UD9W (4P675765-1A) ↗ · 4P675765-1A · page 248 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026