CARRIER DIAGNOSTIC REFERENCE STATUS LED — SHORT + LONG FLASH CODES DOC CARRIER-34

Carrier furnace: Code 34 — Ignition Proving Failure

Q: What does code 34 mean on a Carrier furnace?

Code 34 — Ignition Proving Failure. No flame proved during the trial for ignition; the control retries 3 more times before lockout 14. Official checklist: flame sensor must not be grounded, oxide buildup (clean with fine steel wool), proper microamps (0.5 min, 4.0–6.0 nominal), gas valve on, igniter health, inlet gas pressure.

YOUR LIGHT: 3 SHORT + 4 LONG FLASHES — MATCH IT ABOVE

DIY-friendly fix

What does code 34 mean on a Carrier furnace? No flame proved during the trial for ignition; the control retries 3 more times before lockout 14. Official checklist: flame sensor must not be grounded, oxide buildup (clean with fine steel wool), proper microamps (0.5 min, 4.0–6.0 nominal), gas valve on, igniter health, inlet gas pressure.

Gas / CO warning

This condition involves the gas or combustion side. If you smell gas or a CO alarm sounds: leave, then call your gas utility. Diagnostic info here is reference — combustion repairs are for licensed technicians.

GOOD NEWS: THE FIRST CHECKS ARE FREE AND TAKE MINUTES.

Try these first — in this order

Clean sensor, confirm the igniter glows, check the gas valve is on — 20 minutes.

1Check: Oxidized flame sensor — clean with fine steel wool (official)

2Check: Defective hot-surface igniter (should glow orange-white in 15 s)

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

Pressure adjustment and valve replacement. DIY part cost: $8–18 / $20–40 — a pro visit for this class of fault typically runs $150–350.

What causes it (in order of likelihood)

Oxidized flame sensor — clean with fine steel wool (official) DIY-CHECKABLE
Defective hot-surface igniter (should glow orange-white in 15 s) DIY-CHECKABLE
Gas valve off/defective, low inlet pressure TECH

Parts referenced by this code

LH33WZ511 — Flame Sensor

$8–18 · also sold as LH33WZ515 · Verify fitment for your model

Amazon HVACDirect

LH33ZS004 — Hot Surface Igniter

$20–40 · also sold as LH33ZS003 · Verify fitment for your model

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.37/49

Last verified 2026-07-06 · how we verify