Rheem Error Code A121: Bypass Valve Error

Severity
Warning
Type
digital display
Where to look
front panel
Estimated repair cost: $100 — $350 (parts + labor)
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

  1. Check and clean the air filter. A clogged filter can cause system malfunctions.
  2. Verify that the outdoor unit is running. If not, check the thermostat settings and ensure power is reaching the unit.
  3. If the system is still not functioning correctly after these steps, call a professional HVAC technician.

How to Reset Rheem Code A121

  1. Turn off the unit using the power button on the front panel.
  2. Turn off the gas supply valve.
  3. Turn off the circuit breaker supplying power to the unit. Wait 30 seconds.
  4. Restore power at the breaker, then open the gas valve.
  5. Turn the unit back on. If the error returns, the underlying issue needs repair.

What does 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.

Affected Models

Replacement Parts

PartOEM NumberEst. Cost
Bypass Valve Assembly RJ011127 —
Reversing Valve Assembly RJ011128 —

Related Codes on Same Models

CodeDescriptionSeverity
A001 Ignition Failure Warning
A003 Abnormal Ignition Warning
A004 False Flame Detection Warning
A008 Exhaust Temperature High Warning
A011 No Flame Detected 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