H0 on a Daikin Altherma LT: Sensor abnormality

What it means

The manual says: Sensor abnormality.

Part involved: thermistor / pressure sensor.

When it shows: ■ The detected valve of the supply voltage and the DC voltage is obviously low or high. ■ The compressor current doesn't run when the compressor is started | The detected valve of the supply voltage and the DC voltage is obviously low or high. The compressor current doesn't run when the compressor is started. 3 3.

Likely causes:

• Reactor disconnection; Compressor disconnection; Outdoor unit PCB defective; Compressor defective.

Is it safe?

The manual does not say whether the heat pump stops.

Resetting itself: unknown.

Manual reset: Reset via the remote controller (Inspection/Test button) after the cause is fixed; some codes need a manual reset of the remote-controller memory (service manual section 1.4).

What you can check

• Read the full error code shown on the user interface and note it, with the date/time, for your installer.

What the engineer will check

• Follow the service-manual troubleshooting flow chart for this code: check reactor disconnection; check compressor disconnection; check outdoor unit PCB defective; check compressor defective.

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

• No heating
• Intermittent fault

What owners and engineers report

1 owner and engineer report mentions this.

• No heating on the Altherma LT (low temperature split): 1 report

Sources

• Service Manual ALTHERMA ERHQ006~008BAV3 / ERLQ006~008BAV3(9) / EKHBH(X)008BA (ESIE10-02) ↗ · ESIE10-02 · page 171 · Reviewed 23 September 2026

A code explains what the controller detected, not a confirmed root cause.

Reviewed: 23 September 2026