Carrier furnace code 45: Control Circuitry Lockout
Professional repair
What does code 45 mean on a Carrier furnace? Auto-resets after 1 hour. Official causes: gas-valve relay stuck open, flame-sense circuit failure, or a software check error. Reset power to clear; replace the control if it repeats.
Before you touch anything: the six signs that mean stop troubleshooting and call a pro →
GOOD NEWS: THE FIRST CHECKS ARE FREE AND TAKE MINUTES.
Try these first — in this order
One power-cycle (30 s) is the official reset.
If code 45 returns, the board gets replaced. DIY part cost: $120–250 — a pro visit for this class of fault typically runs $150–350.
What causes it (in order of likelihood)
- Control board internal fault TECH
Parts referenced by this code
Always match parts against your model's parts list — part numbers vary within a series.
Questions about this code
What does code 45 mean on a Carrier furnace?
Auto-resets after 1 hour. Official causes: gas-valve relay stuck open, flame-sense circuit failure, or a software check error. Reset power to clear; replace the control if it repeats.
How do I fix Carrier furnace code 45?
Causes include a stuck gas-valve relay, a flame-sense circuit failure, or a software check error. Don't keep resetting it; if it returns, a technician should diagnose the control.
How much does it cost to fix Carrier furnace code 45?
Cost depends on whether the lockout recurs. If it does, the manual points to replacing the control, and parts availability and labor will shape the price.
Applies to
58STA · 58STX
Different Carrier generations use different code maps. If your series isn't listed, don't assume this meaning — check your blower-door label.
Same control platform, same code: Bryant furnace code 45 · Payne furnace code 45
Verified against Carrier 58STA/58STX Installation & Service Instructions (1106202L), p.37/48
Last verified 2026-07-06 · page updated 2026-10-03 · how we verify
Other Carrier furnace codes
These links include other Carrier model families. Code meanings can change by model and control board, so confirm your model and service manual before using a definition.