H6-00 on a Daikin Altherma: OU: Malfunction of position detection sensor
Short answer
On a Daikin heat pump, H6-00 means: OU: Malfunction of position detection sensor. 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: OU: Malfunction of position detection sensor.
Part involved: thermistor / pressure sensor.
When it shows: Compressor fails to start within 15 seconds after the compressor run command signal is sent.
Likely causes:
- Faulty compressor or miswiring of the compressor power supply cable.; Faulty main PCB.; Closed stop valve in the refrigerant circuit.; Clogged refrigerant circuit.; Refrigerant overcharge or shortage.; Non‑condensables and/or humidity in the refrigerant circuit.; ▪ Faulty or disturbance of the power supply (power supply MUST be within range of nominal operating voltage ±4%), ▪ Power drop, ▪ Short circuit.
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 after a continuous operation of 10 minutes. Manual reset via 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.
- 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
- minutes. If the error re-occurs within 8 minutes: unit will stop operating. Manual reset via user interface. ; Perform a check of the compressor. . ; Perform a check of the main PCB. . ; Check that all stop valves of the refrigerant circuit are open. . ; Check if the refrigerant circuit is clogged. . ; | Troubleshooting ; Check if the refrigerant circuit is correctly charged. . ; Check for the presence of non‑condensables and/or humidity in the refrigerant circuit. . ; Check if the power supply is compliant with the regulations. .
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
11 owner and engineer reports mention this.
- No heating on the Altherma: 7 reports
- Intermittent fault on the Altherma: 2 reports
- Unusual noise on the Altherma: 2 reports
Sources
- Service manual Daikin Altherma 3 M EBLA/EDLA04~08E (ESIE22-09) ↗ · ESIE22-09 · page 56 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026