Carrier · A niche brand in the UK. 30 codes across 2 product families, each taken from the manufacturer’s manuals. Carrier technical support ↗
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Type the code on your display or a word from its meaning. Each code opens its own page with what it means, whether it is safe and what you can check.
30 codes
| Code | Meaning | Stops? | Homeowner check? |
|---|---|---|---|
| 2 | Safety input (external alarm input pin 21-3 closed: unit off, water pump off) | Yes | Yes |
| 3 | Frozen plates exchanger (plate heat exchanger froze during cooling); restart only by power OFF-ON after qualified check | Yes | Yes |
| 4 | Actual refrigerant temperature sensor (TR) | Yes | Yes |
| 5 | Outdoor air sensor of GMC | Varies by model | Yes |
| 6 | Loss communication to NUI control | Varies by model | Yes |
| 7 | NUI control room sensor | Varies by model | Yes |
| 8 | Unit capacity mismatch | Yes | Yes |
| 9 | Flow switch error / water pump | Yes | Yes |
| 10 | EEPROM corrupt | Yes | Yes |
| 11 | User interface setting mismatch | Partly | Yes |
| 12 | 4-way valve error | Yes | Yes |
| 13 | Loss communication to RS485 (system configuration type 6) | Varies by model | Yes |
| 14 | Loss of signal from inverter board or high temperature release | Yes | Yes |
| 15 | Exit water temperature sensor (LWT) | Yes | Yes |
| 16 | Alarm test | No | Yes |
| 17 | Inverter air sensor (TO) | Varies by model | Yes |
| 18 | G-Tr inverter short-circuit protection | Yes | Yes |
| 20 | Compressor position detection circuit error | Yes | Yes |
| 21 | Inverter current sensor error | Yes | Yes |
| 22 | Heat exchanger sensors (TE)/(TS) | Yes | Yes |
| 23 | Discharge temperature sensor (TD) | Yes | Yes |
| 24 | Outdoor fan motor error | Yes | Yes |
| 26 | Other unit error | Yes | Yes |
| 27 | Compressor lock | Yes | Yes |
| 28 | Discharge temperature error | Yes | Yes |
| 29 | Compressor breakdown | Yes | Yes |
| 30 | Low pressure system error | Yes | Yes |
| 31 | High pressure system error | Yes | Yes |
| E3 | NUI communication failure: NUI has not received CCN communications for 60 s; temperature display shows E3, time area '-', outside temp blanked | Partly | Yes |
| E4 | NUI EEPROM failure: all installer/user settings revert to factory defaults after power cycle; no field fix - thermostat must be replaced | Partly | Yes |