| Code | Meaning |
|---|---|
| U4 | Communication (transmission) failure between the indoor and outdoor unit |
| UC | Centralized control address duplication |
| UE | Malfunction in communication with centralized control |
| 80 | Entering water temperature thermistor malfunction |
| 81 | Leaving water temperature thermistor or drain pipe heater malfunction |
| 8H | Abnormal hot water high temperature |
