Carrier furnace Status code 33: Limit circuit fault — a limit or flame rollout switch is open
Code 33 means a limit or flame rollout switch is open. The blower runs for four minutes or until the switch remakes, and if it stays open beyond three minutes the code escalates to lockout 13.
Applies to: Carrier 58MCB four-way multipoise condensing gas furnaces and related models using the same integrated furnace control. Bryant and Payne furnaces of the same generation use the same control and code set.
What it means
This code covers two switches with very different implications. A high limit opening means the furnace is overheating, which is usually an airflow problem and usually mundane. A flame rollout switch opening means flame escaped the burner compartment, which is serious. Carrier's documentation groups them because they share a circuit, and it notes the critical operational detail: the flame rollout switch requires manual reset. So if the furnace recovers on its own, a limit was involved; if it stays down until someone presses a button, rollout was. That distinction is worth establishing before deciding how urgently to act.
Most common causes
- A dirty filter or restricted duct system, which Carrier lists explicitly.
- A restricted vent.
- Improper vent sizing.
- Excessive wind.
- A loose blower wheel.
- A defective blower motor or capacitor.
- A defective switch or its connections.
- Inadequate combustion air supply, which Carrier specifically associates with the flame rollout switch opening.
How to diagnose it
- Check the air filter first. Carrier lists it among the causes and it is the most common.
- Establish whether a rollout switch is involved. If the furnace will not restart until a button is pressed, it is rollout and the situation is more serious.
- Note whether the blower runs for four minutes after the fault, which matches Carrier's documented behaviour.
- Walk the house and check for closed or blocked registers and a clear return grille.
- Note whether the code escalates to 13, which means the circuit stayed open beyond three minutes.
How to fix it
- Replace the air filter and open closed registers. This resolves a large share of limit circuit faults.
- If a flame rollout switch has tripped, stop and call a technician. Do not press the reset button — the switch tripped because flame went somewhere it should not, and resetting without finding out why puts the furnace straight back into that condition.
- Blower motor faults, a loose blower wheel, duct problems, and vent restrictions are technician work.
- Have working carbon monoxide alarms on every level of the home and outside each separate sleeping area, which is what NFPA 720 and US Consumer Product Safety Commission guidance call for. That includes the level the furnace is on — basements, attics and utility spaces are where a combustion fault starts, and an alarm only on bedroom floors can miss it for a long time. This fault is one of the situations those alarms exist for.
Notes
The manual reset on the flame rollout switch is the clearest signal in this code. Every other safety in the circuit resets itself; that one requires a person, precisely so the condition gets investigated.
Related
All codes for this manufacturer
Carrier, Bryant and Payne furnace status codes — every code, with what differs between models.
Code 33 vs code 13 — one circuit, two codes
Carrier gives the limit circuit two codes and puts the entire difference in timing. Both come from the same wiring: on this chassis the high limit switch (LS) and the flame rollout switch (FRS) sit in series in one circuit, per the service manual's schematic, so the control cannot electrically tell them apart — it only sees the circuit open.
| Code 33 | Code 13 | |
|---|---|---|
| What happened | A limit or rollout switch opened; the control is in a fault, not a lockout | The same circuit stayed open longer than 3 minutes |
| Blower | Runs 4 minutes or until the open switch remakes, whichever is longer | Still running — the 4-minute minimum outlasts the 3-minute escalation point |
| How it ends | The switch remakes and the code stops with the blower — or 3 minutes pass and it escalates to 13 | Auto-resets after 3 hours; Carrier's table refers diagnosis back to 33 |
| The rollout exception | The flame rollout switch requires manual reset, so a rollout trip never remakes on its own — it presents as 33 escalating to 13, then a furnace that stays down until the button is pressed | |
Which switches and models this covers
From the cited 58MCB service manual (327884-101 Rev. B):
| Item | What the manual documents |
|---|---|
| Furnace family | Carrier 58MCB four-way multipoise fixed-capacity condensing gas furnaces, sizes 040–120, Series 110 and 120 — plus Bryant and Payne furnaces of the same generation using the same control |
| High limit switch (LS) | Opens on overheat and remakes once temperatures fall, which is why a plain limit event can clear itself |
| Flame rollout switch (FRS) | Manual reset, single-pole, normally closed, per the wiring legend — a rollout trip stays tripped until a person resets it |
| Board variants | Both red and amber LED boards use this code; red boards lose stored codes when power is interrupted, so read before resetting anything |
Do it yourself or call a technician?
Split the decision by which switch tripped, because the two halves of this code carry very different risk. The limit half is where homeowner work lives: filter, registers, return grille — cheap, documented causes, no tools, no cabinet opened. The rollout half is where it ends. If the furnace stays down until a reset button is pressed, flame left the burner compartment, and the manual-reset design exists precisely so a person investigates before the furnace runs again — pressing it yourself defeats the one safety in this circuit that demanded human attention. In between sit the blower causes Carrier lists (loose wheel, failed capacitor or motor): live-cabinet electrical work, professional. The honest rule for code 33: you may fix airflow; you may not reset flame.
The same fault, split apart on other brands
Carrier folds into one code what most control families keep separate. The open-limit half maps to Goodman's 4 flashes and Lennox alert 250, among the 17 open-limit codes across 11 families. The rollout half gets a dedicated code almost everywhere else — Goodman's 6 flashes, Lennox 200, a hard lockout, Allied's 8 flashes. On those brands the code itself tells the technician which switch opened; on this Carrier control, the manual-reset behaviour is the only thing that does.
What the fix costs
Priced from the repair cost guide, the outcomes ladder up. A limit switch runs $150–350, with the guide's caution that the visit must find why it tripped rather than just change the part. The blower causes Carrier lists sit at $150–350 for a run capacitor and $400–700 installed for a PSC blower motor — which is what this chassis uses — per the blower motor cost guide. And a rollout investigation that reaches the heat exchanger lands at $1,000–2,500+, the point the repair guide calls the usual replace-the-furnace moment — which is exactly why a rollout trip is a symptom to chase, never a nuisance to reset. More rollout equivalents across brands: rollout switch codes.
What this looks like
From the outside, this usually shows up as the furnace heats then trips out on high limit — that walkthrough covers what to check in order, and when it stops being a homeowner job.