H0-00 on a Daikin Altherma: OU: Voltage/current sensor problem
Short answer
On a Daikin heat pump, H0-00 means: OU: Voltage/current sensor problem. 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: OU: Voltage/current sensor problem.
Part involved: thermistor / pressure sensor.
When it shows: Compressor voltage (DC) is out of range before start‑up.
Likely causes:
- Faulty main PCB.; ▪ Faulty or disturbance of the power supply (power supply MUST be within range of nominal operating voltage ±4%), ▪ Power drop, ▪ Short circuit. Prerequisite: Stop the unit operation via the user interface. Prerequisite: Turn OFF the respective circuit breaker.; Thermal interface grease NOT applied properly on the heat sink.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: no.
Manual reset: 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.
- 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
- | Troubleshooting ; Perform a check of the main PCB. . ; Check if the power supply is compliant with the regulations. . ; Wait until the rectifier voltage is below 10 V DC. DANGER: RISK OF ELECTROCUTION Confirm the rectifier voltage is below 10 V DC before proceeding, see " To prevent electrical hazards " [4 254 ] . ; Check that the thermal interface grease is applied properly on the (PCB or refrigerant piping) contact surface of the heat sink. Adjust if needed.
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
- Service manual Daikin Altherma 3 M EBLA/EDLA04~08E (ESIE22-09) ↗ · ESIE22-09 · page 53 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026