Heat pumps · Error codes · Daikin
J7-12Daikin · Altherma 3 WS (water source)
J7-12 on a Daikin Altherma 3 WS: Brine inlet thermistor abnormality
Short answer
On a Daikin heat pump, J7-12 means: Brine inlet thermistor abnormality. 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: Brine inlet thermistor abnormality.
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
Sources
- Installer reference guide Daikin Altherma 3 WS EWSAH/EWSAX-UD9W (4P675765-1A) ↗ · 4P675765-1A · page 250 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026