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H9-00

H9-00 — OU: Malfunction of outdoor air thermistor

Daikin · ASHP Error Codes

What does H9-00 mean?

The thermistor (temperature sensor) measuring the outdoor air temperature in the outdoor unit (OU) is malfunctioning.

Common Causes

  • Defective outdoor air thermistor
  • Damaged wiring
  • Sensor blockage

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Ensure the outdoor air thermistor is clean and unobstructed.

  2. 2

    Check the wiring connected to the thermistor.

  3. 3

    Restart the unit.

  4. 4

    If the issue persists, contact a service technician.

Browse all codes in this manual (60)
Verified technical data. Last updated: April 2026

Related Faults

7H-017H-01 — Water flow problem7H-047H-04 — Water flow problem during domestic hot water production7H-057H-05 — Water flow problem during heating/sampling
Source: Daikin ASHP Error Codes
Open Manual (Page 3)Search more codes in this manual