Heat pumps · Error codes · Daikin
CJ-02Daikin · Altherma
CJ-02 on a Daikin Altherma: Room temperature sensor problem
Short answer
On a Daikin heat pump, CJ-02 means: Room temperature sensor problem. The heat pump keeps running. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Room temperature sensor problem.
Part involved: user interface / room thermostat.
When it shows: User interface room thermistor input is out of range.
Likely causes:
- Faulty room thermistor.; Faulty wiring between the remote controller and the unit.; Faulty hydro PCB.
Is it safe?
| Does the heat pump stop? | No |
|---|---|
| Severity | Warning |
| Engineer needed? | Yes |
The heat pump keeps running.
Resetting itself: yes.
Manual reset: Automatic reset.
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.
- 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 room thermistor: ▪ Measure the room temperature and compare to the room temperature shown on the user interface (remote controller). ▪ If temperature shown on the user interface differs from the measured temperature, replace the user interface (remote controller). See documentation of the user interface (remote controller) for more information. ; Check the communication wiring between the remote controller and the unit. . ; Perform a check of the hydro PCB. .
Who to ask for: Heat pump installer (Daikin-trained).
Certification: None specific; MCS-certified installer recommended.
What you might notice
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 40 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026