Daikin Altherma fault U0-00

What it means

Refrigerant shortage detected in the outdoor unit refrigerant circuit; unit will stop operating.

Likely causes

1. Faulty refrigerant side thermistor(s)
2. Faulty refrigerant pressure sensor
3. Closed stop valve in the refrigerant circuit
4. Clogged refrigerant circuit
5. Refrigerant shortage
6. Non-condensables and/or humidity in the refrigerant circuit
7. Faulty compressor or miswiring of the compressor power supply cable
8. Faulty expansion valve
9. Leak in the refrigerant circuit
10. Incorrect refrigerant charge
11. Faulty suction thermistor
12. Blockages in refrigerant circuit
13. Poor water flow through high pressure side plate heat exchanger
14. High pressure switch confirmed faulty during checking procedure

Where to start

1. Perform a check of all refrigerant side thermistors
2. Perform a check of the refrigerant pressure sensor
3. Check that all stop valves of the refrigerant circuit are open