Carrier Furnace 33 Error
What it means
On a Carrier gas furnace, the amber status LED reports faults as a flash pattern — code 33 shows as three short flashes, a pause, then three more flashes, repeating. Code 33 means LIMIT CIRCUIT FAULT: a safety switch (the high-limit switch or a flame-rollout switch) has opened because the furnace got too hot or detected flames where they should not be. The control board shuts the burners off to protect the heat exchanger and your home. The overwhelming cause is poor airflow — heat builds up inside the furnace because air is not moving across it fast enough. If the same condition lasts more than 3 minutes, Carrier escalates this to a hard lockout shown as code 13.
The bottom line on the 33 error
Code 33 usually means an airflow problem — a dirty filter or blocked vents overheating the furnace until a safety switch trips — not a failed part. But this is a gas furnace: a repeating 33 can hide a cracked heat exchanger or flame rollout, a carbon-monoxide hazard, so a code that keeps returning means stopping and calling a licensed HVAC technician.
The safe first move is free: fit a fresh, correctly sized filter and open the registers. A failed limit switch is a cheap repair, but never bypass it, and leave gas-side work to a pro.
33 snapshot
This is a gas furnace — a repeating code 33 can hide flame rollout or a cracked heat exchanger, a carbon-monoxide hazard, so shut the furnace off and call a licensed HVAC technician; never bypass a limit or rollout switch.
Our own at-a-glance triage of the 33 error, from the verified data on this page. See error-code rankings → · How we score →
Common causes of the 33 error
- Dirty or clogged air filter, or a filter with too high a MERV rating that chokes airflow
- Closed, blocked, or too few supply/return vents and registers reducing airflow through the furnace
- Blower motor or blower wheel problem (dirty wheel, failing motor, bad capacitor) so not enough air is moved
- Dirty or partially blocked evaporator (A/C) coil sitting above the furnace restricting airflow
- Flame rollout caused by a cracked heat exchanger or blocked burners (a serious safety condition)
- A genuinely failed high-limit or rollout switch that opens when it should not
Which Carrier furnaces get the 33 error
Code 33 (three amber flashes) is reported by Carrier gas furnaces with the LED status-light control board — the Comfort, Performance, and Infinity series — and the near-identical Bryant and Payne furnaces built on the same platform, which share the flash-code system.
How to fix the Carrier Furnace 33 error
- 1Replace the air filter firstTurn the system off, pull the filter, and inspect it. A dirty filter is the number-one cause of code 33. Install a clean filter of the size your furnace specifies. If you recently switched to a high-MERV (very dense) filter and the code started, try a lower-restriction filter — some furnaces cannot pull enough air through very dense filters.
- 2Open and unblock the ventsWalk the house and make sure supply registers and return-air grilles are open and not covered by furniture, rugs, or boxes. Restricting airflow makes the furnace overheat and trip the limit. Aim to keep most registers open.
- 3Let it cool and resetMost high-limit switches reset automatically once the furnace cools. After clearing the airflow restriction, turn the power off for 30 seconds and back on, then call for heat and watch whether the furnace completes a full cycle without re-tripping.
- 4Check the blower and coil are cleanLook (with power OFF) at the blower compartment for heavy dust on the blower wheel. A caked blower wheel or a dirty A/C coil above the furnace both starve airflow. These usually need professional cleaning, but you can confirm whether they look dirty.
🧰 When to call a professional
Call a licensed HVAC technician if the filter and vents are clear but code 33 keeps returning, if the furnace escalates to a lockout (code 13), if you smell anything unusual, or if you suspect flame rollout or a cracked heat exchanger — a cracked heat exchanger is a carbon monoxide hazard and the furnace should be shut off until inspected. A gas furnace carries gas, carbon monoxide, and high-voltage risks. Never bypass or disable a limit or rollout switch; have a professional handle blower, gas-side, and heat-exchanger repairs.
Carrier 33 vs Goodman 3 Flashes vs Rheem 3 Flashes: how they compare
How this code stacks up against related error codes for difficulty, urgency, and cost.
| Carrier 33 | Goodman 3 Flashes | Rheem 3 Flashes | |
|---|---|---|---|
| DIY difficulty (1–5) | 5 | 5 | 5 |
| Urgency (1–5) | 5 | 4 | 5 |
| Typical cost | $$ | $$ | $$$ |
How much does it cost to fix the 33 error?
| DIY fix (replace air filter, open vents) | Free–$30 |
| Professional repair (limit / rollout switch) | $100–$400 |
| Blower or evaporator-coil cleaning | $120–$600 |
| Replacement (new furnace installed) | $3,000–$7,500 |
Repair or replace?
Code 33 is an airflow warning far more often than a broken part, so start with the free fixes — a fresh filter and open vents clear the large majority of cases at no cost. If a switch genuinely failed, it is an inexpensive repair worth doing on any furnace. The only time replacement enters the picture is when diagnosis reveals a cracked heat exchanger causing flame rollout: on a furnace past roughly 15 years, that carbon-monoxide hazard usually justifies a new unit rather than a repair.
Common replacement parts for the 33 error
| Air filter (correct size, standard MERV) | $5–$30 | The #1 fix for code 33 | |
| High-limit switch | $4–$150 | Part cheap; $150–$400 installed | |
| Flame rollout switch | $15–$60 | If overheating tripped rollout | |
| HVAC diagnostic / service call | $75–$210 | Per visit; higher after hours |
Prices are typical retail ranges and vary by model and supplier — always confirm the exact part number for your appliance before buying. We are not linking parts for this code on purpose: it is a job for a qualified technician, and the right fix here starts with a diagnosis, not a purchase.
Carrier 33 error — FAQ
＋ − What is the difference between Carrier code 33 and code 13?
Code 33 is the active Limit Circuit Fault — the safety switch is open right now. Code 13 is the Limit Circuit LOCKOUT: if the code-33 condition persists for more than about 3 minutes, the board locks the furnace out for safety (typically a 3-hour auto-reset, or you can reset by cycling power). In short, 13 is the escalation of 33.
＋ − I just installed a thicker, high-MERV filter and got code 33 — is that the cause?
Very likely. Dense high-MERV filters can restrict airflow enough to overheat the furnace and trip the limit. Try a standard-efficiency filter of the correct size, or have a technician confirm your blower can handle the higher rating.
＋ − Will the furnace fix itself after code 33?
Sometimes — most high-limit switches reset automatically once the furnace cools, so it may run again. But it will keep tripping until you fix the underlying airflow problem, and repeated tripping can lead to a code-13 lockout. Treat it as a real fault, not a one-off.
Sources & manufacturer references
This guide is independently written and not affiliated with Carrier. Always unplug appliances before servicing and follow your model's manual. Error codes and steps can vary by model — when in doubt, consult a qualified technician.