Daikin Altherma fault L4-00

What it means

Radiating fin thermistor measures a too high temperature, causing the unit to stop operating.

Likely causes

1. Faulty outdoor unit fan motor
2. Faulty or disturbance of power supply (power supply MUST be within range of nominal operating voltage ±4%)
3. Power drop
4. Short circuit
5. Faulty inverter PCB
6. Faulty main PCB
7. Thermal interface grease NOT applied properly on the heat sink
8. Deviation of thermistor (higher temperature measured than actual).
9. Faulty room thermistor
10. Bad contact between sensor and pipe
11. Loose or disconnected wires
12. Damaged connectors or wires
13. Deviation of outlet water after backup heater thermistor (lower temperature measured than actual)
14. Deviation of thermistor (lower temperature measured than actual)
15. Bad contact between refrigerant loop and inverter heat sink
16. Lack of refrigerant
17. LD1 not flashing: no operation of LAN adapter
18. LD2 flashing: TCP/IP communication problem with router
19. LD3 flashing: communication problem between LAN adapter and indoor unit

Where to start

1. Perform a check of the outdoor unit fan motor
2. Check if the power supply is compliant with the regulations
3. Perform a check of the inverter PCB