CARRIER DIAGNOSTIC REFERENCE STATUS LED — SHORT + LONG FLASH CODES DOC CARRIER-45

Carrier furnace: Code 45 — Control Circuitry Lockout

Q: What does code 45 mean on a Carrier furnace?

Code 45 — Control Circuitry Lockout. 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.

YOUR LIGHT: 4 SHORT + 5 LONG FLASHES — MATCH IT ABOVE

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.

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.

Still showing the code? See every cause ↓ Get repair quotes near you

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

HK42FZ034 — Furnace Control Board

$120–250 · also sold as HK42FZ013

Amazon HVACDirect

Always match parts against your model's parts list — part numbers vary within a series.

Applies to

58STA · 58STX · Bryant 310/311/312 series · Payne PG8M series

Different Carrier generations use different code maps. If your series isn't listed, don't assume this meaning — check your blower-door label.

Verified against Carrier 58STA/58STX Installation & Service Instructions (1106202L), p.37/48

Last verified 2026-07-06 · how we verify