Temperature sensor
Common error-code part. Confirm resistance and connector style.
Heat Pump Error Codes: All Brands Guide
Heat pumps fail in a few predictable ways no matter whose badge is on the cabinet: high pressure, low pressure, defrost problems, sensor faults, communication failures, and compressor protection. Brand-specific codes change, but the physics do not.
Common Heat Pump Error Codes Across Brands
| Symptom / Code | Common Meaning | Typical Brands |
|---|---|---|
| High pressure | Dirty coil, indoor airflow issue, or overcharge | Carrier, Trane, Goodman, Lennox |
| Low pressure | Low charge or restriction | Carrier, Goodman, Daikin, Rheem |
| Defrost fault | Sensor, board, or outdoor coil icing issue | Trane, Goodman, Lennox, Mitsubishi |
| Communication fault | Indoor and outdoor control issue | Communicating and inverter systems |
| Sensor fault | Ambient, coil, or discharge sensor failed | Most inverter systems |
| Compressor protection | Overcurrent, overtemp, or overload | Most brands |
Cooling vs heating matters
A pressure fault in cooling points you toward the outdoor coil or refrigerant. The same style fault in heating may point toward the indoor coil, blower, or defrost performance.
Defrost is a major differentiator
Straight AC systems do not have to manage frost. Heat pumps do. If a heat pump ices up outside and then shuts down, defrost sensors, defrost boards, or refrigerant charge become prime suspects.
Inverter heat pumps protect themselves earlier
Variable-speed heat pumps will often throw discharge temp, sensor, or drive protection codes before they ever get to a hard mechanical failure.
Step-by-Step Fix
- Pull the exact code — Do not troubleshoot based on symptom alone.
- Check coils and airflow — Indoor and outdoor airflow still solve a lot of heat pump problems.
- Consider operating mode — Heating and cooling faults mean different things on the same machine.
- Review defrost behavior — If the outdoor coil stays iced, the defrost system needs attention.
- Use gauges if qualified — Pressure and charge faults need real measurements.
- Retest in both modes — A true fix should survive both heating and cooling operation if seasonal conditions allow.
Parts and Tools Often Needed
| Item | Notes |
|---|---|
| Defrost board | Common on standard split heat pumps |
| Defrost sensor | Cheap but important |
| Run capacitor | Still common on non-inverter systems |
| Contactor | Voltage drop and no-start complaints |
| Thermistors | Frequent on inverter units |
| Coil cleaner | Essential before condemning parts |
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 heat-pump faults, match parts to the code family: thermistors, pressure switches, defrost sensors, capacitors, contactors, fan motors, reversing-valve coils, or outdoor control boards.
Need Replacement Parts?
Before ordering, match the HVAC part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
When to Call a Pro
Heat pump codes that point to low refrigerant, compressor protection, or repeated defrost failure deserve a qualified tech. Heat pumps are harder to diagnose casually because the same circuit has to work correctly in two opposite modes.