Rheem Error Code A099: PCB Failure

How to Fix Rheem Code A099

1. Step 1: Turn off the system at the thermostat and the breaker or disconnect switch. Wait 5 minutes, then turn it back on. If the code clears, a temporary power glitch may have caused it, but still schedule a check.
2. Step 2: Check the thermostat wiring at the wall. Ensure no bare wires are touching. If you have a nest or other smart thermostat, try pulling it off for 1 minute to reset communication.
3. Step 3: If the code returns immediately after power-up, or the system still won't start, call a Rheem HVAC pro. Do not attempt to open the electrical panel or replace the board yourself—it requires proper configuration and safety checks.

How to Reset Rheem Code A099

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.

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 A099 Mean?

The A099 error on Rheem systems indicates a failure of the main control board (PCB). This board controls all system functions, including ignition, fan speed, temperature sensing, and communication with thermostats. When it fails, the system cannot operate correctly or at all. This is typically a hardware failure—often a relay stuck open or closed, a failed capacitor on the board, or a burned trace from a power surge. It can also be triggered by a low-voltage short from the thermostat or zone panel. The board itself is not user-serviceable; it must be replaced by a qualified technician. On Rheem gas furnaces (like the R801T) and air handlers (like the RH2T), this error usually locks the system out, meaning it won't attempt to start again until power is cycled or the thermostat calls again. On Rheem heat pumps (like the RP16), it may also disable the outdoor unit.

Common Causes

• Failed control board components (relays, capacitors, or transformer) due to age or power surge
• Low-voltage short in thermostat or zone panel wiring that damages the board
• Incorrect wiring or loose connections between the board and system components
• Condensate leak or water damage inside the equipment cabinet shorting the board

Diagnostic Steps

Replacement Parts

Related Codes on Same Models

Other codes that affect the same Rheem model families as A099.