Carrier furnace: Code 33 — Limit Circuit Fault
Try DIY first, then call a pro
What does code 33 mean on a Carrier furnace? A limit, draft safeguard, flame rollout, or blocked-vent switch is open. The blower runs 4 minutes or until it closes; open >3 minutes escalates to lockout code 13. Rollout and BVSS switches need a manual reset.
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
Filter + every vent open — 5 minutes, the most common self-fix.
If the rollout switch tripped, get a tech before resetting anything. DIY part cost: $5–25 / $10–25 — a pro visit for this class of fault typically runs $150–350.
What causes it (in order of likelihood)
- Dirty filter or restricted ducts (official first cause) DIY-CHECKABLE
- Restricted vent, excessive wind, loose blower wheel TECH
- Defective blower motor or capacitor TECH
- Inadequate combustion air → flame rollout switch open (CO-risk signal) TECH
Parts referenced by this code
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