Daikin Altherma fault HA-00

What it means

Malfunction related to outdoor heat exchanger thermistor sensor; unit stops heating and cooling operation until resolved.

Likely causes

1. Faulty outdoor heat exchanger thermistor
2. Faulty main PCB
3. Deviation of thermistor (higher temperature measured than actual).
4. Faulty room thermistor
5. Bad contact between sensor and pipe
6. Deviation of outlet water after backup heater thermistor (lower temperature measured than actual)
7. Deviation of thermistor (lower temperature measured than actual)
8. Incorrect refrigerant charge
9. Faulty expansion valve control
10. Faulty suction thermistor
11. Blockages in refrigerant circuit
12. Faulty discharge pipe thermistor
13. Domestic hot water tank thermistor measures a higher temperature than actual (component failure)

Where to start

1. Perform a check of the outdoor heat exchanger thermistor
2. Check discharge pipe thermistor.
3. Measure the room temperature and compare to the room temperature shown on the user interface (remote controller)