Daikin Altherma fault H9-00

What it means

Outdoor air thermistor input is out of range.

Likely causes

1. Faulty ambient air thermistor
2. Faulty main PCB
3. Deviation of thermistor (higher temperature measured than actual).
4. Faulty room thermistor
5. Deviation of thermistor (lower temperature measured than actual)
6. Bad contact between sensor and pipe
7. Deviation of outlet water after backup heater thermistor (lower temperature measured than actual)
8. Domestic hot water tank thermistor measures a higher temperature than actual (component failure)

Where to start

1. Perform a check of the outdoor air thermistor
2. Perform a check of the main PCB
3. Check discharge pipe thermistor.