Daikin Altherma fault C4-00

What it means

Refrigerant liquid thermistor detects an open or short circuit during compressor operation.

Likely causes

1. Faulty refrigerant liquid thermistor
2. Faulty hydro PCB
3. Faulty room thermistor
4. Deviation of thermistor (higher temperature measured than actual).
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)
14. Incorrect or missing software on the PCB

Where to start

1. Perform a check of the refrigerant liquid thermistor
2. Perform a check of the hydro PCB
3. If all procedures listed above have been performed and the problem is still present, contact the helpdesk