Rheem Error Code A021: Over-Temperature
Warning: Your Rheem HVAC system has detected an overheating condition. Turn off the system and call a professional for repair.
How to Fix Rheem Code A021
- Turn off the system at the thermostat and at the circuit breaker
- Do not attempt to open the unit or perform any repairs yourself
- Contact a licensed HVAC technician for diagnosis and repair
How to Reset Rheem Code A021
- Turn off the unit using the power button on the front panel.
- Turn off the gas supply valve.
- Turn off the circuit breaker supplying power to the unit. Wait 30 seconds.
- Restore power at the breaker, then open the gas valve.
- Turn the unit back on. If the error returns, the underlying issue needs repair.
Resetting clears the code from the display but does not fix the underlying fault. If the code returns after reset, proceed to the diagnostic steps above.
What Does Rheem Error Code A021 Mean?
The A021 error code on your Rheem HVAC system indicates that the unit has reached an unsafe temperature. This is likely due to a malfunction in the system's temperature control or a problem with the cooling components. The system has automatically shut down to prevent damage or safety hazards. It's important to address this issue promptly to avoid further damage or potential safety risks.
Common Causes
- Faulty temperature control board or sensor
- Clogged or dirty condenser coils
- Low refrigerant levels
- Failed compressor or fan motor
Diagnostic Steps
| If... | Check | Expected |
|---|---|---|
| System is not running | Check for power at the compressor and fan motors | No power |
| System is running | Measure temperature at the evaporator outlet | Below 40°F (4°C) |
| Temperature is above 40°F (4°C) | Inspect and clean condenser coils | Clean coils with no signs of damage |
| Coils are clean and temperature is still high | Check refrigerant pressure | Pressure within manufacturer's specifications |
Applicable Rheem Models
- NCB(gas)
- NPE(electric)
- R801T(gas)
- R92E(electric)
- R92V(gas)
- RGE(gas)
- RH2T(electric)
- RNC(dual_fuel)
- RNE(electric)
- RNG(gas)
- RP16(electric)
- RPB(gas)
- RTGH(gas)
- Rheem Classic(gas)
- Rheem Classic 80 Plus(gas)
- Rheem Classic 80% Gas Furnace(gas)
- Rheem Classic 90 Plus(gas)
- Rheem Classic Plus Series(gas)
- Rheem Classic Series(dual_fuel)
- Rheem Prestige(gas)
- Rheem Prestige 95% Gas Furnace(gas)
- Rheem Prestige Series(gas)
Replacement Parts
| Part | OEM Number | Est. Cost | Where to Buy |
|---|---|---|---|
| Temperature Control Board | RHEEM 4505229 | — | Find Part |
| Compressor | RHEEM 4502775 | — | Find Part |
| Refrigerant | — | — | — |
Related Codes on Same Models
Other codes that affect the same Rheem model families as A021.
| Code | Description | Severity |
|---|---|---|
| A001 | Ignition Failure | Warning |
| A031 | Inlet Thermistor Open/Short | Warning |
| A041 | Outlet Thermistor Open/Short | Warning |
| A043 | Water Level Error | Warning |
| A051 | Fan Motor Abnormality | Warning |
| A052 | Fan Motor Speed Error | Warning |
| A053 | Fan Motor Open Circuit | Warning |
| A054 | Fan Motor Overcurrent | Warning |
| A055 | Fan Motor Locked | Warning |
| A095 | DIP Switch Error | Warning |