Geothermal pressure switch
Match refrigerant type, trip pressure, connector, and Carrier model before replacing a lockout pressure switch.
$20-$80
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Carrier Geothermal Heat Pump Error Codes
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 against the model manual; 1.5 GPM/ton is a common starting target, not a universal limit
- 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 entering water temperature against the installation manual; many Carrier geothermal units expect EWT below 85°F, but the limit is model-specific.
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 from the loop design or service manual; 20-25% is common in many climates, but the required freeze protection is site-specific
- Loop pump operation
- Entering water temperature compared with the model’s freeze-protection threshold; about 25°F is common, but not universal
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 |
| Condensate float switch | Check drain-pan layout and wiring style |
Technician Tips
Carrier uses different diagnostic systems across furnaces, heat pumps, chillers, mini-splits, VRF equipment, rooftop units, and communicating controls. Confirm the full model number and whether the fault came from the indoor board, outdoor board, thermostat, or equipment controller before matching it to a repair path.
Start with power, wiring, airflow or water-flow, sensor, condensate, and safety-circuit checks before ordering control boards. If the same code returns after one reset and the basic cause is not obvious, test the named circuit instead of repeatedly cycling the equipment.
Parts note: For geothermal heat-pump faults, match parts to the water-loop or refrigeration circuit involved: flow switches, thermistors, pressure switches, condensate parts, control boards, or blower components.
Focused Parts Searches
Before ordering, match the HVAC part to the model number, electrical rating, and failure symptom:
- Carrier geothermal pressure switch
- Carrier geothermal ECM blower motor module
- Geothermal loop circulator pump
- 10K geothermal water temperature sensor
- HVAC condensate float switch
Prices and availability change frequently.
Pro tip: Carrier Infinity geothermal units store fault history in the Infinity control. Navigate to System > Advanced > Fault History to view timestamped fault records.