Carrier Geothermal Heat Pump Error Codes: Complete Guide
Carrier geothermal heat pumps (Infinity GHP and Performance series) communicate faults via the Infinity system control or the on-board diagnostic LED. This guide covers all common Carrier geothermal fault codes.
Carrier Geothermal Fault Code Table
| Code | Description | Common Cause |
|---|---|---|
| 1 | Low-pressure lockout | Low refrigerant, low airflow, low loop flow |
| 2 | High-pressure lockout | High loop temp, dirty coil, overcharge |
| 3 | Freeze protection trip | Low loop temp, low water flow |
| 4 | Condensate overflow | Clogged condensate drain |
| 5 | High discharge temperature | Low refrigerant, restricted TXV |
| 6 | Compressor protection — high amp | Locked rotor, low voltage |
| 7 | Compressor protection — low voltage | Check supply voltage |
| 11 | Freeze stat fault | Loop antifreeze concentration low |
| 12 | Low ambient lockout | Ambient below unit minimum |
| 13 | Coax (water coil) freeze protection | Low loop water flow or temperature |
| 21 | ECM blower fault | Failed ECM motor or module |
| 22 | Communication fault | Wiring between Infinity control and unit |
| 24 | Control board fault | Replace control board |
| 31 | Refrigerant circuit fault | Pressure switch or refrigerant issue |
| 33 | Lockout — manual reset required | Multiple faults — identify root cause |
| 41 | Leaving water temperature fault | Water sensor issue |
| 42 | Entering water temperature fault | Water sensor issue |
Most Common Carrier Geothermal Faults
Code 1 — Low-Pressure Lockout
- Check air filter and blower operation
- Check loop pump operation and flow rate (minimum 1.5 GPM/ton)
- Check entering water temperature
- Check refrigerant charge with gauges
Code 2 — High-Pressure Lockout
In cooling: high loop water temperature is the primary cause. Check EWT — should be below 85°F for most Carrier geothermal units.
In heating: dirty air coil, failed blower, or airflow restriction.
Code 3 — Freeze Protection
Loop water temperature is too low, or antifreeze concentration is insufficient. Check:
- Propylene glycol concentration (should be 20–25% for most climates)
- Loop pump operation
- EWT — below 25°F triggers freeze protection on most models
Code 22 — Communication Fault
Carrier Infinity geothermal units communicate via the Infinity bus. Check:
- All control wire connections at the unit and thermostat
- Infinity control for error messages
- Polarity of the communication wires
Code 21 — ECM Blower Fault
ECM (variable-speed) motors fail as a module or the motor itself. Test:
- Supply voltage to the ECM module
- Control signal from the control board
- Replace ECM module first (lower cost) before replacing full motor
Carrier Geothermal Parts Reference
| Part | Notes |
|---|---|
| Low/high pressure switch | Match refrigerant type and trip pressure |
| TXV assembly | Model-specific — match refrigerant and capacity |
| ECM blower motor | Match HP and model — Carrier GHP specific |
| Loop pump | Grundfos or Bell & Gossett — match GPM |
| Freeze stat | Check setpoint — typically 30°F |
| Water temperature sensor | 10K thermistor — check resistance curve |
Pro tip: Carrier Infinity geothermal units store fault history in the Infinity control. Navigate to System > Advanced > Fault History to view timestamped fault records.