Bryant 355MAV Error Code 45: Control Circuitry Lockout
What Does Code 45 Mean?
Status code 45 on the Bryant 355MAV indicates a control circuitry lockout. The control board has detected an internal failure and locked itself out for 1 hour as a safety precaution. This lockout can be caused by a flame sense circuit failure, a gas valve relay stuck open, or a software check error within the control board.
A flame sense circuit failure means the board's internal circuitry for reading the flame sensor signal has malfunctioned. This is different from a dirty flame sensor or bad wiring — the problem is on the board itself. A gas valve relay stuck open means the internal switch on the board that sends power to the gas valve cannot close, preventing the furnace from opening the gas valve to start combustion.
You can attempt to clear this lockout by turning off power to the furnace for 30 seconds and then turning it back on. If the furnace resumes normal operation, the issue may have been a one-time software glitch. However, if code 45 appears again after resetting, the control board has a persistent internal failure and will need to be replaced by an HVAC technician.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Flame sense circuit failure on control board | Most common | ✗ Call a pro → |
| Gas valve relay stuck open | Common | ✗ Call a pro → |
| Software/firmware check error | Uncommon | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- Code 45 returns after resetting power — the control board likely needs to be replaced
- The furnace locks out repeatedly with code 45 even after successful power resets
✓ Verified against manufacturer service manual — March 2026