Carrier 58MVC Error Code 45: Control Circuitry Lockout
What Does Code 45 Mean?
Status code 45 on the Carrier 58MVC is a control circuitry lockout that occurs when the board detects an internal failure. This auto-resets after one hour, but the underlying causes — flame sense circuit failure, gas valve relay stuck open, or a software check error — all point to problems within the control board itself.
The flame sense circuit on the board is responsible for detecting whether the burner flame is present. If this circuit fails, the board cannot safely manage ignition. Similarly, a gas valve relay that is stuck open means the board cannot energize the gas valve to allow gas flow, even when conditions are otherwise correct for ignition.
As an immediate step, you can try resetting power to the furnace by turning it off at the breaker for 30 seconds and then turning it back on. If the code clears and does not return, it may have been a one-time software glitch. However, if status code 45 reappears after the reset, the control board is failing and needs to be replaced by a qualified technician.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Flame sense circuit failure | Common | ✗ Call a pro → |
| Gas valve relay stuck open | Common | ✗ Call a pro → |
| Software check error on control board | Uncommon | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- If the code reappears after a power reset — the control board likely needs replacement
- If the furnace fails to operate after resetting power
✓ Verified against manufacturer service manual — March 2026