Rheem Error Code A121: Bypass Valve Error
Warning: Your Rheem HVAC system has encountered a bypass valve error, which may cause comfort issues. It's safe to troubleshoot, but if not resolved, call a professional.
How to Fix Rheem Code A121
- Check and clean the air filter. A clogged filter can cause system malfunctions.
- Verify that the outdoor unit is running. If not, check the thermostat settings and ensure power is reaching the unit.
- If the system is still not functioning correctly after these steps, call a professional HVAC technician.
How to Reset Rheem Code A121
- 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 A121 Mean?
The A121 error on your Rheem HVAC system indicates a problem with the bypass valve, which is part of the reversing valve assembly. This valve switches the refrigerant flow between heating and cooling modes. When it malfunctions, your system may not switch modes correctly, leading to comfort issues. The error code A121 usually means the valve is stuck in one position or not responding to commands.
Common Causes
- Faulty bypass valve or reversing valve assembly
- Low refrigerant charge
- Wiring or electrical issues
- Control board or sensor malfunction
Diagnostic Steps
| If... | Check | Expected |
|---|---|---|
| Outdoor unit is not running | Thermostat settings and power at outdoor unit | Thermostat set to 'Heat' or 'Cool' and power present at outdoor unit |
| Refrigerant pressure is low | Refrigerant charge | Normal refrigerant charge for system type and size |
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 |
|---|---|---|---|
| Bypass Valve Assembly | RJ011127 | — | Find Part |
| Reversing Valve Assembly | RJ011128 | — | Find Part |
Related Codes on Same Models
Other codes that affect the same Rheem model families as A121.
| Code | Description | Severity |
|---|---|---|
| A001 | Ignition Failure | Warning |
| A021 | Over-Temperature | 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 |