Bryant 340MAV Error Code 45: Control Circuitry Lockout
What Does Code 45 Mean?
Code 45 on the Bryant 340MAV is a control circuitry lockout. The integrated furnace control board has detected an internal fault in its own logic or sensing circuitry. The board will automatically attempt to reset after a 1-hour lockout period. Cycling power can also clear the lockout temporarily, but the code will repeat until the underlying cause is resolved.
The service documentation identifies two triggers: a gas valve relay stuck open on the control board, and a software check error. A stuck-open relay means the board's internal switching component for the gas valve remains in an active state when it should not, causing the board to detect an inconsistency in its own control logic. A software check error is a firmware self-test failure.
The service documentation explicitly instructs: reset power to clear the lockout and replace the control if the status code repeats. Because the fault is internal to the board, no external component repair will resolve it.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Gas valve relay stuck open on control board | Most common | ✗ Call a pro → |
| Software check error on control board | Common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- If the code returns after the 1-hour auto-reset, the control board needs replacement — contact a technician
- Do not attempt to repair or modify the control board; it must be replaced as a complete unit
✓ Verified against manufacturer service manual — March 2026